I grew up with the internet as an everyday part of life from my mid-teens onwards. Back then, we were taught to be careful about what information we give out online because there are no backsies and you can never be sure who you're talking to.
Not sure when that changed to "give out all your personal info and it'll probably be fine somehow" on a lot of these sites, but personally I stick with the former approach wherever I am. I'm not totally anonymous, far from it, but I only share what I don't mind being public.