The existence, not the result, of the poll is the message
what if anything at all might these poll results show?
It doesn't really matter what percentages were reported in the poll. Adams is offering a hot take on the numbers, but he didn't really need the numbers to be what they are in order to make an argument.
The real point is that the poll was conducted at all. This shows that American political discourse has reached a point where innocuous questions can be used to provoke superficially absurd responses, and that push-pollers (Rasmussen aren't really push-pollers, but they aren't exactly held in the highest possible esteem among pollsters either) can reliably provoke such a response. The question sounds absurd on its face. It's meant to. You're meant to take away the message that claims that should be insignificant are actually highly controversial, purely for the reason that Americans feel a certain compulsion to signal political loyalty. And it's easy to promote this narrative, exactly because it is true.
Political trolling is generally satirical
In the video from Tuesday that led to backlash, Mr. Adams, who is white, said he had “started identifying as Black” years ago
Of course, it would be hard to believe that Mr. Adams is sincere in this identification. There's no sign that he's presented any kind of evidence of such heritage, and some sources I found even state straight out that he's joking about this. There's nothing about his appearance that would register as anything other than "white" to a typical Western person (although I have known Americans to apply the label "black" to people that I cannot possibly imagine as such).
But that absurdity is exactly the point. Adams is satirizing the concept of "identification", implicitly arguing that an individual's "identification" (i.e., personal perception of the self) does not change reality, and that moreover such labelling will be blithely ignored by others in favour of their own perception of that individual. The quote from NYT perfectly illustrates this: by saying "who is white", NYT claims authority to judge Adams' race, and marks his claimed identity as illegitimate.
By pushing the media to commit to that position, Adams exposes the hypocrisy of, for example, those who defended Elizabeth Warren's claim to indigenous status. (As a reminder: while Warren's DNA test - taken at Trump's goading - did technically turn up some indication of indigenous ancestry, it was at a level that is not at all unusual for Americans generally deemed "white", and which convincingly put the lie to the specific details of Warren's claims. I should also note here that caring about that DNA test at all inherently accepts the notion that race is genetic, which runs counter to the narrative that people talking about race as a "social construct" or "not real" seem to be trying to build.)
At the same time, the capitalization in this quote highlights another common talking point for Adams and others with similar politics. We see a stark juxtaposition: in concordance with their style guidelines, NYT here has capitalized "black" but not "white". (We know that this is a deliberate choice on NYT's part because they are quoting from a video, not from Adams' writing.) It's hard not to see this as, at best, a petty attempt to score culture-war points, and at worst a sincere expression of the notion that black people are somehow inherently superior to white people (something that rational, unbiased people would ordinarily call "racism" or "black supremacy", but which increasingly many, increasingly-mainstream sources refuse to label as such).1
Since Adams is an important enough figure in American culture war to expect the article to be written in the first place, and because of his experience with said culture war, it would have been easy for him to predict that NYT would produce a quote along these lines, which would allow him and his supporters to further the narrative of bias.
None of this is unusual or unexpected from Adams; this is his MO and he's quite up-front about it in his own writing. It's also consistent with, for example, his previous comics in which he portrayed a black character who "identifies as white" in the same spirit, to troll the PHB. (Perhaps "Dave" perceives that the PHB has taken him on merely to meet the "diversity" requirement cited in the first comic, and does not see him as a capable worker in his own right.)
The reaction to this was predictable: critical outlets proposed that this is an expression of transphobia (despite that Adams never mentioned anything here about gender, simply critiquing the concept of self-identification is treated as a cryptic attack), and they simultaneously laughed about the comic losing the skin coloration when reproduced in black-and-white newspapers while complaining about him taking so long to include any "people of color" in his comic.
While I haven't checked for a response, I can easily imagine ways in which Adams could continue the act. For example, what if several of his characters have in fact been "of color" all along? Why should he have to disclose which ones? And why should he have to use shading to indicate a character's race (is that term not itself problematic)? As for the comic looking different in colour vs. black-and-white, that could easily be portrayed as a deliberate irony. Adams is well known for his "two movies" framing of culture war (essentially: everything is filtered through the lens of individual experience, thus it is not actually possible for people to have "the same facts"), and the comic appearing with Dave literally appearing clearly different from the other characters in only some renderings (but substantially the same in others) would be an ideal illustration (pun intended) of the concept.
Culture-war slogans are inherently bait, which makes them trolling
The purpose of saying "Black Lives Matter" clearly extends beyond the literal meaning of the words. I don't simply mean that it signals affiliation in the culture war. I mean that saying something that is innocuous on its face, in a political context, carries the implication that some other people must disagree (or it wouldn't need to be said; politics is argument about policy) and therefore that such people constitute The Hated Outgroup. That is, it is not only a claim about oneself, but about others. I've seen any number of video clips and sound bites of activists explicitly charging that some other specific individual "thinks black lives don't matter" (which can also be seen as the ideological continuation of Kanye West's charge that "George (W.) Bush doesn't care about black people", which promptly became a protest song).
A similar analysis argues that "All Lives Matter" carries the implicit claim that certain other people believe that only certain lives matter (with the context implying that "certain other people" = BLM activists and "certain lives" = lives of black people). As you note, this analysis is broadly incorrect; relatively few people - of any race - carry enough racial hatred with them to literally believe that the deaths of certain people might not have any meaning, according to their race.
However, stopping the analysis there would be facile. After all, as I just said, relatively few people would actually agree with such a claim applied to black people. It should be clear that almost everyone in the US sees other people as humans with rights, regardless of their race, and would rank death as among the worst things that can happen to a person, and murder as clearly a serious crime regardless of the race of the victim (or perpetrator).
So, again - that's the point. By introducing a countering slogan, one inherently implies the invalidity of the premise of the first slogan. That is: the implicit argument is that the BLM activists are implying a falsehood. Similarly: by setting up the slogan to be maximally inclusive (they didn't even specify human lives, for that matter, although it's generally understood), those using the ALM slogan (they cannot really be called activists, as they exist to counter existing activism rather than to propose a specific policy change) can portray themselves as morally virtuous (i.e., not discriminatory).
Please stop taking the bait
With this analysis framework in mind, understanding the coinage "it's OK to be white" is trivial. The obvious goal is to insinuate that some people believe the opposite, i.e., that there is somehow something inherently wrong with "being white".
As established in the first section, most Americans would consider the fact of "being white" to be a consequence of one's birth (i.e., genetic, although the categorization admits subjectivity) which is immutable and not the result of the individual's agency. This, of course, stands in stark contrast with academic theories of "whiteness", which generally appear to revolve around considering "white identity" as not a simple observation of the skin tone of individuals but as some inherent motivation to a racist worldview.2
So, when the phrase is put out there, and actually manages to generate any controversy as a result, the implication for third-party observers is clear: that there are, apparently, people lurking around who think that white people are inherently inferior (presumably, morally inferior), as a consequence of something about themselves that they cannot change. Again: rational, unbiased people would normally call this "bigotry", specifically "racism" as it is done on the basis of race.
A mature, rational response to "all lives matter" does not look like what we've seen from BLM activists. (Of course, being activists, they have a vested interest in generating controversy and drawing attention to their cause - not in discussing issues sincerely.) It looks like: "Yes; so you agree that the lives of black people, being lives of people, also matter. We are concerned specifically with XYZ things happening to black Americans, which we believe happens in American society in a racially disproportionate way and further that this disproportion is the result of institutional biases; would you like to discuss this?" (Again, of course, this is far too long for a sound bite.)
Similarly, a mature, rational response to "it's okay to be white" is, more or less, to ignore it. People who do not already believe in the racial supremacy of white people, are not going to start believing it because of the "propaganda" of being told "don't worry, it's not in fact the case that your mere existence is unacceptable". A not-already-racist white person who notices such a sign isn't being convinced to become racist, but simply resonating with a resentment of how the racial discourse in American politics has changed.3
Nobody likes being identified with a group and subsequently demonized on the basis of membership in the group, especially when such membership was not freely chosen. That is, after all, the point of the discourse around racism. Racism is bad particularly because people don't get to choose their race, and thus they are being blamed for something out of their control. It's not bad because of the things racists do while citing their racist beliefs as a justification - just like how crimes committed by activists (of any stripe) don't invalidate their causes.
If a response really is necessary, a mature response looks something like: "of course; we don't assert otherwise", followed by a clear explanation of the actual arguments around "whiteness" that got people to the point where the IOTBW posters could actually draw any attention. (Of course, it would have to be an argument that actually doesn't involve white people being inherently morally inferior. I am not at all convinced that the academics in question don't actually believe that. The more I try to engage with their writing, the harder it becomes to believe that they have an actual non-bigoted point.)
It certainly does not look like "oh, no, to heck with that, You are Not Okay (and there's nothing you can do about it)".
1I feel compelled to include something here about how the media feels entitled to describe the words or actions of individuals as "racist" - which is to say, making it into an objective, factual claim, reported in news rather than analysis or opinion, and simply in passing as if this were not a moral judgment but a simple observation of the natural world. In reality, of course, racism is far more of a "social construct" than race itself.
1From what I can tell, this is entirely disingenuous; I am confident that none of these supposed academics would grant that a white person could in principle "stop being white", and you can see this from the accusations of transphobia lobbed at both Adams and at more serious academics - but I digress.
2I can't let this point pass without highlighting the way that white people who complain about this deluge of negative messaging - the constant association of one's race with Bad Things - will get yet another negative message in return. As I write this, I can already imagine the people who wish to respond to me in such a manner.
I could also say so much here about the actual demonstrated fragility of various marginalized groups; or the hypocrisy of people who promote "implicit association tests as evidence of "implicit bias" but don't think any of this overt messaging should count as evidence of their own bigotry; or the hypocrisy of explicitly engineering biased terminology while closely analyzing organically evolved English for bias - sometimes without heed to actual etymology; or the hypocrisy of academics using their position of power as academics, to promote the memes (in the original sense) that they do about "privilege"... but you get the idea. The short version is, the academics in this field come across to me as profoundly intellectually dishonest - and the people goading them, likely sense that as well.