Another example of an absurd question like that was one I was asked when I was applying for my visa; along the lines of "are you planning to commit espionage for another country against the United States". I assume they do it so they can pin you for perjury as well was whatever crime you committed should you turn out to be a spy. But it's just so absurd when asked deadpan like that.

The reason for those is to then quickly provide a way to invalidate their visa and have an administratively easy path to kick them out without having to go to court and such. Terrorist activities doesn't mean blowing things up, it could be open to all kinds of interpretation (donated money to some organization, protested and was arrested for rioting, went to a black-hat conference which had talks about subverting security systems of power plants etc, etc).

Any statue establishing those could also establish that those are proper cause for immediate deportation, no need for fancy forms and logic-gymnastics.

They're just getting you to incriminate yourself. The standard of proof for excluding someone for lying on the forms is quite different from convicting them of an actual terrorism-related crime.

Sure that question is dumb, but it's not at all comparable to forcing you to turn over a password. Why would you make that false equivalence?

Because you can as easily create a fake social media profile

Those are just to make people easily deportable if they're found to have lied.

So if such person engages in a terrorist act having lied on a form would matter at all?