Well, such laws became "unconstitutional" only when the Supreme Court decided in the 1980s that flag desecration laws were unconstitutional. Believe it or not, but most people thought prior to that decision that such laws were constitutional, and, in fact, such laws were enforced.
While it is awesome to see liberals now embrace the value of stare decisis, that has not always been the case, i.e., 30 days ago. Lest we forget that point, let us all reflect on noted liberal Constitutional Law Professor Mark Tushnet's rant from May of 2016, when he was licking his chops at the prospect of lining up social conservatives and shooting them in the back of the head:
" A jurisprudence of “wrong the day it was decided.” Liberals should be compiling lists of cases to be overruled at the first opportunity on the ground that they were wrong the day they were decided. My own list is Bakke (for rejecting all the rationales for affirmative action that really matter), Buckley v. Valeo (for ruling out the possibility that legislatures could develop reasonable campaign finance rules promoting small-r republicanism), Casey (for the “undue burden” test), and Shelby County. (I thought about including Washington v. Davis, but my third agenda item should be enough to deal with it.) Others will have their own candidates. What matters is that overruling key cases also means that a rather large body of doctrine will have to be built from the ground up. Thinking about what that doctrine should look like is important – more important than trying to maneuver to liberal goals through the narrow paths the bad precedents seem to leave open."
Now, as a result of our experience in dealing with liberal totalitarians of this sort, I have a greater appreciation for freedom of speech, but what do we do when the wheel turns and these kinds of people are back in power? Do we simply apply our principles now and then let them apply theirs when they have power, and thereby experience the gradual ratcheting toward a left totalitarianism?
I never thought that the Republic would fall, or free speech would be substantively burdened by flag desecration laws. I always thought that Americans needed a symbol that was outside of politics to rally around. I also have noted that in the last thirty years, the left elite has been fine with mocking the symbols of the average American while demanding that its own sacred things be off limits and shielded with safe spaces and speech codes.
I think tearing down the left's carefully constructed system of things that cannot be desecrated might be the best option, but listen to the screams when that happens.