I simply don't understand the complete lack of self esteem that would make one in this culture want to permanently deface his or her own body in order to: a) fit in, b) stand out, c) emulate felons, or d) freeze yourself into a fashion that is counterproductive and unflattering. But then again, I don't "get" multiple piercings and gauging, either. These are people who aren't confident enough to stand as themselves, without artifice, and have to make their costumes (or masks) speak for them. Sad.
Ignorance is probably the best explanation.
I think the recent popularity of tattoos is analogous to the grooming choices of the 60s generation, and has the same kind of "I want to prove to everyone that I think for myself" motivation. Or maybe it's from all the magazines skimmed by the barely literate children who say "whatever" when they don't have a coherent response. ;')