Which is why, while I can see the appeal on a number of levels, it just seems like it's going to end badly VERY often. I keep thinking of an FML I read a while back where a grown person found out the "family friend" who'd been doing everything with their parents all their lives, even going on family vacations, was actually a third spouse, and everyone in town knew except that person. Nothing like finding out at age 25 that you don't know who your biological father is.

For all that, I don't think it should be illegal; people screw their lives and their childrens up in all sorts of perfectly legal ways. Divide everything by the number of departing spouses instead of automatically dividing by two. Perhaps a little more legal paperwork would be necessary going into it to prevent problems when it fell apart (as, I still maintain, it almost certainly would) but the real problem there is the extent to which we've let personal matters related to marriage bleed into civil laws.