In America, there has been more acceptance of liberal leaning issues, such as marijuana legalization and gay marriage. Though democrats have been found to be more accepting of these issues, the surveys have found republicans and independents as well becoming more accepting of socially liberal issues, including those two. Is this true?
The NYT has analyzed the Republican Party and found that it has slightly moved to the right since 2000. Note that the Republican Party stood already far to the right of conservative parties in Western Europe and Canada.
Pew Research observed a move to the right from 1994 to 2014 among Republican voters as well.
FiveThirtyEight has also noticed a rightwards shift among Republican voters as well as Republican congressmen from 1976 to 2012.
The move can be seen in the rise of the Tea Party, Donald Trump and his association with the far right, a rise in support of antisemitic conspiracy theories, etc. As you specifically mention gay marriage, the GOP remains strongly against it.
It's really not possible to understand things like this on a left-right scale, since they're essentially libertarian issues. To a certain kind of leftist/liberal, they might be anathema because they (supposedly) interfere with societal productivity &c*. Likewise, to the limited government kind of conservative – as opposed to the religious right/social conservative – things like that aren't the government's business as long as you don't do it in the street and scare the horses.
The bottom line is that, despite rhetoric from extremists on such issues, people in general have become more accepting of them, therefore the mainstream of the parties has to reflect that (while still appeasing their extremists), or lose the votes of the middle. And neither party can win an election with only the votes of its committed membership.
*Or just because adopting socialist/Marxist economic policies doesn't mean you necessarily abandon ingrained prejudices. See any of numerous articles on the treatment of gay people in various Communist & Socialist countries, for instance.
Liberal is a direction, away from "here", not a destination.
Since gay marriage is the law of the land, supporting it is literally conservative; conserving the status quo instead of changing it. Any change now would be liberal. Wanting to change the current laws on abortion (or anything else) is a liberal position. In that respect, the country actually becomes more conservative as formerly-liberal ideas become mainstreamed.
In some sense, this sounds backwards, or like playing with semantics, but you have to step above any current battles to spot the historical arc.
Generally people in democracies tend to get things they want over time, so they become more conservative as they age. Youths are less accustomed to prior concessions, so they tend to advocate for more change from "here", which makes them liberal. Education offers insight into means of improving (aka changing), which means that the educated are often more liberal than the not. People who serve put their life on the line for a country that's good enough to die for as-is, so changes aren't as appealing, thus they skew conservative. Disadvantaged people have incentives to change the status quo to more benefit them, making them liberal.
Thus there's no long-term trend towards more liberal or more conservative; they ebb and flow in response to events. You can correlate such a mood using surveys of "right/wrong direction". If "right direction" is high, society is conservative (satisfied). If "wrong direction" is higher, then society at the time is more liberal (wanting change).
Under that rubric, I suppose an argument could be made that satisfaction trends down, and thus the country becomes more liberal, but not in the manner your question assumes.
Assuming that by “more liberal”, you mean towards opinions that have recently been associated with the Democratic party. Which does not necessarily correspond to self-identification as “liberal”/“conservative” or “left”/“right”, or to non-US definitions of “liberal”.
Pew Research Center asked Americans the same 10 questions between 1994 and 2017. and the shifts in opinions are graphed on Page 7. The phrasing of the statements in the chart titles is such that agreeing with them reflects the Republican or “conservative” position.
Over that 23-year period, the shifts within the Republican party have been:
- -21 (58%-37%) on “Homosexuality should be discouraged by society”
- -20 (64%-44%) on “Immigrants today are a burden on our country because they take our jobs, housing and health care”
- -5 (74%-69%) on “Government is almost always wasteful and inefficient”
- -2 (54%-52%) on “Most corporations make a fair and reasonable amount of profit”
- -1 (64%-63%) on “Government regulation of business usually does more harm than good”
- +2 (63%-65%) on “Poor people have it easy because they can get government benefits without doing anything in return”
- +9 (66%-75%) on “Blacks who can't get ahead in this country are mostly responsible for their own condition”
- +9 (44%-53%) on “The best way to ensure peace is through military strength”
- +11 (58%-69%) on “The government today can't afford to do much more to help the needy”
- +19 (39%-58%) on “Stricter environmental laws and regulations cost too many jobs and hurt the economy”
That's a strong shift towards “liberalism” on homosexuality and immigration (even after Trump's “build the wall” campaign), towards “conservatism” on environmental regulations, welfare, and the military, but on average there's not a consistent trend in either direction.
In contrast, the Democratic party has consistently moved towards “liberal” positions.
- -50 (62%-12%) on “Immigrants today are a burden on our country because they take our jobs, housing and health care”
- -29 (42%-13%) on “Homosexuality should be discouraged by society”
- -26 (44%-18%) on “Poor people have it easy because they can get government benefits without doing anything in return”
- -25 (53%-28%) on “Blacks who can't get ahead in this country are mostly responsible for their own condition”
- -16 (46%-30%) on “Government regulation of business usually does more harm than good”
- -15 (28%-13%) on “The best way to ensure peace is through military strength”
- -14 (59%-45%) on “Government is almost always wasteful and inefficient”
- -13 (37%-24%) on “The government today can't afford to do much more to help the needy”
- -11 (35%-24%) on “Most corporations make a fair and reasonable amount of profit”
- -9 (29%-20%) on “Stricter environmental laws and regulations cost too many jobs and hurt the economy”
An average of 20.8 percentage points in the “liberal” direction, with their view of immigrants being the most dramatic shift.
It's impossible to make blanket statements on this sort, because of the nature of modern politics. On one hand we have parties that rely on hard-line issue-driven polemics to motivate their bases. This creates an appearance of political absolutism, like a huge game of tug-of-war where the goal is to pull the general public across to 'our' side by main force. On the other hand, the American public usually gravitates towards a commonsensical laissez faire (don't bug me and I won't bug you) attitude about things. Certain issues — like homosexuality, equal rights, gay marriage, marijuana, etc — have been held up by hard-line political actors as important, world-altering problems, while the general public has gradually acceded that they are non-threatening non-issues. Other issues — like abortion — actually reflect a serious and growing divide. As a loose rule, liberal positions tend to win by default in the long run, because it is difficult for people in democratic societies to maintain positions which clearly deny the rights of others to lead their lives. But that isn't so much a shift towards liberalism as much as stolidly American "Oh, what-ever!" to prolonged argument.
1. commitment to traditional values and ideas with opposition to change or innovation.
Conservatives have always been against change. Whether that be the end of slavery, universal suffrage, legalizing weed or gay people getting married. Sure you can say that conservatives have gotten more liberal. But this is not something new. It's a natural progression of history that has always happened and that will always keep happening. No matter what labels you assign it.