I can totally understand why you feel this way.  I used to feel the same.  Then, a few years ago, a good friend of mine killed himself.  He was married, had three young children and was a respected, successful doctor.  He was down-to-earth, witty as shit, modest, thoughtful.  One of a kind.  Just a very cool dude.  He was also a recovering alcoholic.  In fact, we met in an outpatient program and got each other through some pretty tough times.  There was not a selfish bone in his body and I know he loved his children immensely.  I will ever accept that he was only thinking of himself when he took his own life.  It just wasn't in his nature. 

I think it's important to understand that when people get to the point where they're ready to chose death over life, they are no longer thinking rationally.  They no longer have a realistic view of their place in this world.  They don't comprehend what they mean to others nor do they realize the tremendous impact their death will have on those who care about them.  They have lost all feelings of self-worth.  I think, often, they truly feel they are doing their loved ones a favor by relieving them of a burden. 

It's hard to understand why any loving parent would chose to leave their children.  I get that.  I really do.  I don't condone suicide nor do I think it's the right choice.  I just don't necessarily see it as a selfish act when someone decides it's their only choice.