Are you saying it would have been a good thing for your wife's parents not to reproduce? Where would that leave her and you?
(noted that childhood you described sounds awful, i agree)
Personally, selfishly, the thought of my life without her is depressing, absolutely. But I can love her and yet -- or more precisely, "and so," because it's out of empathy that I feel this way -- I can understand and support her desire never to have existed.