[account42]

> However, I would question whether denying historical facts is an opinion.

Historical facs have a tendency to change based on the current political climate. Which is to say, they are always more like opinions.

Although a better example would be insulting a police officer or politician, which can include as bening things as making fun of them on twitter. Granted, this is more a concern for citizens than it is for tourists so I agree with your assessment that the US border controls are a bigger threat to you as a traveller.