I, too, have thought sometimes that this choice is nobody else's business. However, that said, I have personally seen how much it does hurt other people, who often never seem to recover. (Case in point, I had a student whose dad had done so, and she brought me his letter. She was so upset, even after a good while had passed. Dad can never come back, and she missed him.)

Sometimes it is done in anger, wanting to hurt others. I find that really sad.

Otherwise, I like to think of the ditty that it's a "permanent solution to a temporary problem."

I always think of my family when I'm getting into that mode.

I believe, then, that it generally is a selfish thing.