Am I legally allowed to use the female restroom in public places? Is this a legal issue or an etiquette issue?

Lol. I think it's fine you go into the girls bathrooms, so long as you aren't peeking, which it seems that you're not. And privacy? Really? It's a PUBLIC restroom! You don't have anymore privacy than the stall your in. And who cares if your a guy? Other women are bound to hear the conversations and flatulence, why does it matter that it's a guy?