This may astound you, too. But I am not terribly concerned about my body breaking down and being in constant agony and misery, because if it gets to the point where I'm not satisfied with things I'll just call it a life.
I know I'll have to give it up eventually. But for now I very much enjoy it, it is my one vice of choice and I'm not planning on giving it up any time soon.
But if it makes you feel better, you're both absolutely right. It is a disgusting habit and there is no justifying it. It makes no sense that someone would do this to themselves, and yet I do. I'm a masochist, I think. Much to my parents' dismay.