Don't they learn love isn't forever? Won't they always know that someone they love could leave any time. Can they really understand the difference between parents love for each other and parents love for a child?
See, I think that's a good thing. With the exception of love for children, all relationships should be conditional IMO. I wonder how much the divorce rate would decrease if all couples shared childcare and housework responsibilities 50/50 and if there was an absence of controlling and/or abusive behaviours.
I would cross continents and walk over hot coals for my partner if he needed me because we are a partnership where each tries to give more than they take. I would also be out of the door like a shot if he started taking me for granted or treated me badly, as would he if I did the same. Funnily enough, we don't - primarily because we're both decent people who love each other, but also because we know it won't be tolerated by the other.
If everyone adopted this viewpoint, romantic/family/friendship/work relationships would be so much better and over time enhance society as those who don't live life like this become excluded and thus incapable of modelling these bad behaviours to the next generation.
I think children are capable of distinguishing between types of relationships - it's why they don't disintegrate when leaving behind their nursery assistant, childminder or that year's teacher. Children should have strong, secure attachments with each parent individually, and those attachments should not be rocked by divorce, however much life changes otherwise and is unsettling. A child can be upset and distressed at the loss of the family home/change of school etc, but as long as the parents remain fair to each other and consistent in their relationship with the child, a child will ultimately weather a divorce without any long-term damage. Sometimes this gets a little muddied when couples first separate and poor behaviour is born of frustration and hurt, but it usually settles down as most parents love their children more than they hate their STBX. And this should teach a child that love for children is unconditional and trumps romantic love, actually creating a stronger sense of security.
The problems really start when parents handle divorce badly and one or both start using the child as a pawn. Unfortunately, the truth is that someone capable of behaving like this is almost certainly going to cause issues for a child even when the family is complete, so nothing is actually gained by choosing to stay together for the sake of the children.