For me the main thing is that SI doesn't address your feelings and real problems. It just makes you not care so much for a little while, but the problems get worse in the mean time.

But motivation for me to stop would have to be realizing the effects that it has on other people. It seems like you're only hurting yourself but it isn't true. When you hurt yourself you are also hurting everyone who cares about you, and there are more people who care about you than you think.