Why is marriage such a big deal? Why do some people care deeply enough about marriage to want to expand the historical and traditional definition to include same-sex couples, and others care deeply enough to claim that such an expansion would destroy marriage?
My wife and I were talking this over on Wednesday and one of the points that came up is that marriage is a partnership contract like no other. In a typical business partnership, there is a "shotgun clause" which allows one the partners to terminate the contract by offering to buy out the other. A partnership can be ended unilaterally; and the resolution is fair and final.
Marriage, on the other hand, is a putatively lifelong contract. The rules for terminating a marriage have been jury-rigged on to our legal tradition in the last few hundred years, and then twisted in the last fifty. The concept of alimony makes much more sense when you're talking about a pre-WWII divorce for cause, rather than a modern "no-fault" divorce.
Contrasting marriage to a business partnership point by point, we see that a marriage can be ended unilaterally, like a partnership. But there is no "shotgun" -- no means of pricing the marriage. Instead the marriage assets are divided evenly. And divorce is not final. A court can award alimony and child support, which continue indefinitely. I suppose this is an attempt to fairly value the lifelong commitment promised in the marriage; but the effect is rather nasty.
Alimony (and child support) are initially based on the higher-earning spouse's current income (in the case of child support, the non-custodial spouse; but this is usually also the higher-earning one). As the years pass, they are adjusted to track current income. Or perhaps the higher-earning spouse is malingering by deliberately taking a low-paying job or returning to college? That's OK -- alimony will be based on "imputed income" -- on the amount of money the malingering spouse could have been earning.
Basically, after a divorce, you can wind up with a nondischargeable claim on your ex-spouse's future earning capacity -- and also with the ability to compel this person to work at the best of their ability to support you. Of course the alimony claim can be forgiven by the recipient. In earlier times I believe this was called "manumission".