You don't "have to", but they can deport you and refuse entry in the future in retaliation. It's a variant of the TSA not being able to "compel" you to a search, but they can refuse you from flying.
The premise (non-citizen) is in the question and doesn't need to be repeated. C'mon, this isn't grade school where you have to answer questions by first restating the question in its entirety.
No, but even in grade school, the teacher would get the student to actually answer the question when it is clearly being evaded. Or maybe put the student's name on the board for wasting everyone's time for being obstinate.
