1.) I don't think it's "American" it probably depends mostly on the forum you visit.
2.) No. But that's really because I'm neither stupid nor extravert. I do understand that if I send someone pictures or mesages that he/she could post them anywhere. I bet there are millions of nude pictures (or even videos) on the internet uploaded by disgrunteled exes, maybe even including names and addresses.
How many children post dumb videos on youtube and subsequently end up as a "meme"? Sure it's mostly their own fault and completely preventable. It does happen tho and sites like facebook with terrible security settings and people posting private stuff has made it more prevalent than ever.