If you're at all involved in polyamory, you've probably heard about the court case in Canada that challenges its long-held anti-polygamy law on the grounds that it is unconstitutionally broad. They just finished with closing arguments, so perhaps we'll hear a ruling soon.
I think the case made against this law is pretty good. The harmful behavior that it's purportedly trying to prevent - child marriage, abuse, etc. - are already criminalized, so this law is redundant. Similarly, it makes no distinction between an egalitarian polyamorous relationship and an abusive patriarchal one. I'm sure this was intentional; I imagine the law, despite what is claimed now, was designed to prohibit non-monogamy for the sake of being non-monogamy.
It's easy to say non-monogamy is inherently bad when you're using non-secular morality. Can't really argue with, "God says so." However, the only basis for secular morality is the prevention of harm to self and others. And when you genuinely and vigorously apply secular morality to a lot of our laws governing personal behavior, as Canada seems to be doing a much better job of than the U.S., those laws start to fall apart.
I'm currently too cynical to expect the U.S. to develop a true separation of church and state; I don't think it ever existed, thanks to certain segments of the population who are convinced that a Christian theocracy is the only way to... um... actually, I'm not sure what they're trying to do. Win at life, maybe? Anyway, I think it'll be a long time before we are able to critically examine our laws with a truly secular mindset. But who knows. Apparently a slight majority of U.S. citizens support gay marriage now; something I wasn't expecting for a while. And I didn't expect us to elect a non-white president until I was middle-aged at least (though that seemed to be a "one step forward; one hundred steps back" situation). So maybe I can allow myself to be a little optimistic about this.