I know, Myself included, a lot of people who struggle with this sort of thing. Most of us feel alone. Taking away self harm blogs will not help anything. In fact, It could make it worse for thousands of people.
When I see a picture of someone else's self harm, I don't think there is anything wrong with it. It's not like they are telling others to do the same to themselves. When I see a picture, or someones cuts, for example, It makes me feel less alone. Like I'm not the only person who feels this way.
One of the great things about tumblr is expressing yourself but now I can't even do that. I understand you want to stop the 'promoting' it, well, There is a HUGE difference between having a self harm blog and telling people to harm themselves.
Please , Leave self harm blogs up. They have personally helped me so much, and I know so many young people who rely on them to get through the day.