This seems like an apples/oranges comparison.

The constitution is pretty silent afaik on whether random foreign nationals such as this tourist have any particular rights. Obviously summarily executing or imprisoning them would be a big no-no, but being asked lots of questions and thoroughly searched because they think you're a troublemaker is not uncommon. Being refused entry to a country that isn't yours and being home safe by the end of the day, is quite a few huge leaps away from being locked up in your own country for your speech.

Do I think that incident sounds like a stupid move by CBP if that is the whole story[1]? Yeah. But I disagree that it's proof we're in a fascist dictatorship.

[1] Is it also possible that the government agents didn't overhear him making some flippant comment that made him seem far more dangerous? For instance, "Yeah I can't believe I'm even coming here when that fascist Trump was elected. Wish that bullet hadn't missed." If he had said or done something to cause it to happen, you can bet he would have forgotten to mention it when he recounted his story to The Daily Star.