Whenever I see this thread I want to respond to people's posts but I never quite know what to say.
It's also tough because RI has a very clear policy on not encouraging SI so I don't want my view on it to get my posts deleted. Basically, I don't think SI is inherently a sin; it can be if you make it an idol, but I think the act of cutting isn't by itself sinful. The verse about your body as the temple of the holy spirit was referring to sexual sins and doesn't entirely apply. One way I'd heard it said was that if it takes you further away from God, if it pushes you away from him, then it's a sin. For me, sometimes I do it purely out of boredom and I like the way they look on my arm. In this sense I don't think it's a sin. It's somewhat a gray area.
The reason I think it applies is because it seems so many in this thread are overwhelmed with guilt over cutting. Is it something we should try to stop using to feel better or cope with things, yes, there are other ways God would want us to deal with things. At the same time however letting guilt flood us is only going to make things worse. Moral guilt and feeling guilty are two different things. Moral guilt is the state of being guilty before a perfect God, while feeling guilty is what satan tries to use to make us feel like we're not worthy of going before God and praying. No matter what we do, if we're Christians, God won't love us less. Also, no matter what we do, we're still saved and all our sins, past and ones we haven't done yet, are forgiven. Feeling guilty doesn't help anything.
There's a lot more I could say but that's kind of on my heart now.