Unfortunately sometimes I've actually had to publicly urinate (trust me, LAST RESORT). It's just sort of good to know that if all the restrooms are locked, I can hide in some trees and pray no one will stumble upon me. The surrounding areas are pretty well-hidden. Maybe that makes me irresponsible or piggish, but I'd rather take the chance of being "caught" than peeing in my pants.
I had a friend who actually had to pee at the end of an isolated subway platform b/c it was 3am and there were no restrooms available. He felt terrible doing it...and sure enough a cop spotted him and cuffed him. They ended up letting him go after a small fine, but he felt pretty humiliated. He still agreed it was better than urinating in his pants.