Casually looking up your peers is exactly what you should be doing in my opinion. But I'm not a good person and I'd rather see details like that plastered everywhere. Be an idiot, get what you deserve.
I have a 2004 Gmail account which people like to use as a fake email address when signing up to things. So my address is in the Ashley Madison leak. This is not something I'm comfortable with people knowing without context, so even if it was a policy of "play stupid games, win stupid prizes" I'd get harmed.