I think it depends on the circumstance. If the cop is asking you because he is investigating a situation, then I think you have to. However, if you are just walking down the street with a "Legalize Marijuana" T-shirt and he asks you, and tells you you aren't being arrested, you should be able to walk away. I mean, if you ask if you're being arrested and he says no, then he can't arrest you for walking away right?

I think most people that get in trouble probably do something to instigate the officer, anytime you are dealing with police common sense should be used. It's like when you see videos of guys screaming at a cop "FREE SPEECH FREE SPEECH", and then he gets arrested. From his view he was arrested for nothing, but to others it's obvious he was creating a situation. Walking away isn't creating a situation.