What do you think about public sex?

Yes, of course you think it's unacceptable, offensive, etc. But aren't public areas just that--public? Should we really restrict what goes on in the public square? We allow religious proselytizing and commercial advertising in many streets and public squares. These are offensive practices to some. You will say if I don't like advertising I can just look away or take another route. Doesn't the same principle apply to public sex?