I take your point, TSBG. But surely questions about social liberty are answered by looking at what society permits or restricts, rather than what just at what the law permits or restricts? The law, after all, is just one instrument of social control - and by no means the most effective.
There is a passage in I can’t remember which of Edith Wharton’s novels where a non-American character, living in New York, expects that she will be able to divorce her (deeply unpleasant) husband and have an excellent prospect of making a desirable second marriage. One of the other characters explains to her that “our laws favour divorce, but our social customs do not”. The class of man that she hopes to marry will certainly be reluctant to marry her, as a divorced woman, and she will suffer various other social consequences, should she divorce.
That was then, of course, and this is now, and divorce is much more socially acceptable. In addition, it is legally easier, but these are distinct things.
Similarly, the US has always had strong laws on freedom of speech. But what it is socially acceptable to say or write can and does vary from time to time and from milieu to milieu, and if you are asking question about how socially liberal the US is, that’s what you need to be looking at. If you are marginalised and excluded for saying certain things, then you are not socially free to say them.
It may of course be morally right that you are not free to say them. I have no problem at all with people suffering social exclusion for espousing, say, The Protocols of the Elders of Zion. (And there’s no doubt that a hundred years ago you would have suffered less social consequences for explicit antisemitism than you would today.) But the OP doesn’t ask whether inexorable social liberalisation is or would be a good thing; just whether it’s a thing.
And I think the answer has to be “no”. All societies impose constraints on their members. The particular constraints that are imposed will vary from time to time, so at any time there is always some constraint that is being relaxed or dismantled and, if you just look at that, you may have a sense of constant liberalisation. But if you carry that to its logical conclusion society must eventually cease to function as all constraints disappear. I’m pretty sure that’s not a thing.