Well currently, it's people being denied entry or re-entry to the United States due to the content of their social media accounts. Also, people getting door-knocked by the FBI for making posts on Reddit.
Historically, there won't be trials for this when it gets worse, so there won't be anyone charged or convicted. They will eventually just be murdered by a secret police force.
You’re not being criminally charged and convicted of a thought crime in this situation. You’re just not welcome to join the party. Big difference. Foreigners have no right to enter the USA other than by what the law permits.
Now, I don’t necessarily agree that we should be denying visas to people based on reasonable disagreements with US policy—after all, existing citizens are entitled to share those same opinions! But “crime” means something, and that’s not what this is.
Marketing, largely. But indeed Americans are free to think and write as they please without criminal consequences. They certainly have more protections than the British do (especially around defamation).
Historically, there won't be trials for this when it gets worse, so there won't be anyone charged or convicted. They will eventually just be murdered by a secret police force.