Often I've said, "You say remove the gender restriction on marriage. OK, with that same reasoning, why not remove the number restriction?"
Almost always, the reply was, "Oh, that's ridiculous." Only once was someone honest enough to tell me, "Well, we're not there yet."
Now, we're a little bit closer to there. From CNews:
Canada’s decision to legalize gay marriage has paved the way for polygamy to be legal as well, a defense lawyer said Wednesday as the two leaders of rival polygamous communities made their first court appearance.
The case is the first to test Canada’s polygamy laws.
Yes, it is ridiculous.