While some think it's selfish to not try stay together for the sake of the kids, I think it's madness. How healthy is it to continue trying to raise them in a poisonous atmosphere of dislike, distrust and animosity?
I feel it's much better to part and the kids have a happy home with one parent than a miserable one with two. Kids know - and you don't need to tell them - when things are bad at home, even at a young age.
While the reasons above in the original post are dumb, yes, the irony is that it's probably the other partner who'll end up having a better life being free of such people than the instigator of the divorce, ha!
Life's too short to be in a miserable relationship. If you know it's beyond repair and you can say in your heart of hearts you tried, then leave and begin anew I say.