Speaking as a Conservative, I've also tried to have these arguments and read discussions by people who purport to support Communism. Here is basically what I've found:
The core change surrounding the growth of Communism in recent years is more or less tied to industrialization. In particular, automation. In the past, we needed humans to do jobs. There had to be a person standing at the cash register at the grocery store to take your money. There had to be a person on the assembly line to affix the door to the side of your car. There had to be a driver at the front of your taxi holding the wheel.
Today, these things are becoming less and less true. See, for example, automatic checkout at the grocery store, or specialized robots on assembly lines, or self-driving cars (well, that last one is still in QA, but they're certainly trying their best). Humans aren't needed to perform these jobs anymore. This causes a couple of changes:
1) Higher unemployment, especially of unskilled labourers. If your only employable skill is taking money at a cash register, and no store needs a person to take money at a cash register, then you're both unemployed and unemployable. In addition to this being just generally "bad" (from the point of view of those sympathetic to these people), it's especially worse because these people are the most vulnerable; these jobs tend to be low in reward, both ephemeral and physical, and thus given the choice between this sort of job and skilled labour, most would likely choose skilled labour. Thus, not only are these people unemployed, but they have a very hard time becoming employed, because they have a deficiency (perceived or actual) which prevents them from gaining the skills needed to perform "skilled" labour.
2) Higher production, despite increased unemployment. A factory which used to run on humans, and then fired all the humans and hired robots instead, still continues to run. The output of that factory has not changed, despite the fact that its workforce disappeared. Furthermore, robots do not need things like "sleep", "vacation days", "sick leave", "lunch time", and so on; this allows the factory to run longer and more efficiently than with humans. Not only has the factory decreased its cost, but it has also increased productivity, by firing its humans and hiring robots.
To recap, automation causes increased unemployment but also increased production. According to Communists I've heard and talked to, this means that (I am not saying this is true, but it is what they would quote to you) society would be able to support everyone based on the output of those who are "willing" to work in trades which require humans, plus the output of robots from trades which do not require humans.
What is interesting in the above statement is that word "willing". Communists presuppose that there exists a drive to work which is not limited to making money; a Communist would suppose that, for example, there are people who enjoy farming for the fun of farming, and even if they weren't paid to be farmers, then the rest of us wouldn't starve, because those people just like farming and could provide food for the rest of us. Again, this is what I've heard, not what I think.
Now, presupposing all of the above, Communism makes sense. Allow everyone to simply do what makes them happy. Some of those people will engage in trades which help support the rest of us, because that's honestly what they would like to do. Others may not, and that's ok too. Between those people who actually enjoy doing the things we need them to do (e.g. farming) and the robots doing work that robots can be specialized to do (e.g. manufacturing, low-skill jobs), everyone will get what they need. "From each according to their ability, to each according to their need".
Now, to address your points:
Labor theory of value seems to be empirically inferior to demand pricing.
Pricing and value mean nothing to Communists. If you can have everything you ever wanted without impacting anyone else's ability to also have everything they ever wanted, what's the point of pricing? Pricing is specifically a barrier intended to regulate what people can have, specifically because not everyone can have everything they want. But we presuppose above that everyone can get everything they want, so this point is moot.
(In this answer I equate "want" with "need", this is intentional)
Communist countries seem to tend towards totalitarianism more than their capitalist counterparts.
Not related to Communism. Communism is an economic structure, not a political one. "In theory" it is possible to have a benevolent communist regime; it just hasn't happened yet.
Communist countries seem to have worse environmental records than their capitalist counterparts.
See above. Deflection argument.
Communist countries seem to have lower standards of living in general than their capitalist counterparts.
Because there hasn't been a Communist country which has modern means of production. As noted in MSalters' answer, the first IBM personal computer came out in 1981. The Soviet Union fell in 1989. The technology available to the Soviets was not even close to what it is today. The only Communist experiment country which has existed and has potential reasonable access to modern automation technology is North Korea, and that country has a host of issues which has prevented it from getting those tools. Among them is likely (my supposition) that the government actively wants its citizens to keep their heads in other endeavours such as work so they spend less time thinking about how shitty their lives are and don't start a revolt.
Therefore, one could say that Communism was tried (and failed) in an era in which it was not practical. However, one might say, if it was tried again today, using modern technology and modern sensibilities, it might succeed.