I used to be a cutter, and the reason I did it was because I had a lot of emotional pain on the inside. To get rid of all that inner turmoil, I cut myself to distract my attention to physical pain because it was better than what I was feeling on the inside.
Some people do it for attention, others do it because it's cool, but some, like me, did it because we were hurting. Don't think all cutters are stupid, because we're not. We're just suffering and need some way to let it out. I've gotten help and I don't do it anymore and I'm glad I don't do it... I get tattoos instead now.