How America turned against the First Amendment

This had nothing to do with the internet.

Speech has always been under attack in the US.

Even in the past 100 years from the teaching of evolution in the early 20th century to bans of "obscene" books and films, even bans on what you can say on radio or television, or banning marches and protests by unpopular groups of people.

If anything, the internet has allowed people to circumvent these bans.

That isn't to say recent attacks on free speech should be ignored. But they are not "thanks to the internet".