Can anyone just get inside a campus in the US?

Good question ╮(￣▽￣)╭

For the most part, yes.

Public universities? Yes. That's true of Mexico too. Private in both countries are a different story and usually more stringent.

Yeah, public campuses are typically open like that. In fact, a lot of them have programs for kids, local families, etc. that are held on campus.

it depends. sometimes you’ll need to scam your id but for the most part yes

Depends on the universitybut yes