lightbrite – the point is that if it’s the wife salary that is supporting the family, if there are two wives, then there is double the salary.
And there are not twice as many people, since there is still only one husband. There are no more than double the number of children – in fact there would probably be less than double the number of children.
And the house does not need to be twice as big. (and even if it did, a house that is twice as big should not cost double). You would still only need one of most things – one kitchen, one fridge, one stove, one oven, one washing machine, one dryer, etc.
You could save on babysitting costs since they could take turns.
And most things end up being cheaper per person when you have more people. It would be kind of like the opposite of a divorce situation. Divorces are expensive because you have to maintain two households for one family. Here, you only have to maintain one household for two families, so it should come out cheaper.
Oh, and btw, I think it was a joke (one that I have heard before).