A while back, I wrote a little piece on the euvoluntarity of plural marriage. At the time, I wrote that objections to polygamy were an example of organized question-begging: polygamy is non-euvoluntary because it's not under the aegis of a conventional capacity for exchange, therefore it must remain illegal. Had I been a bit more thorough, I would have mentioned the downside risk of more young men missing out on the marriage market (in an overlapping-generations model, the median marriage age for men increases in a polygynous society; for polyandry, women delay nuptuals in equilibrium). It could be that packs of feral boys would destabilize the peace we've all come to cherish under a regime that permitted plural marriages.
It could be, but somehow, I don't think it's all that likely. There are lots of ways for unwed men to compete for mates. Depending on the prevailing attitudes towards status, competition could be vigorous participation in the labor market, expressions of creativity, hooliganism, political participation, whatever. The point is, simply assuming the worst in the face of proposed institutional change is insufficient. When political scientists say "assume anarchy", it's not a call for worst-first thinking, it's a plea for circumspection (circumspection Tony--get your mind out of the gutter). It's important that a proposed policy change include a survey of what the world looks like with and without the regulation.
In the case of polygamy, the anarchy condition has to recognize that in market societies, competition for mates is often quite peaceful, and can even be positive-sum. I think we'd also have to recognize that in the US anyway, polygamy would be practiced by a vanishingly small minority. If the harms are negligible and the rates of occurrence are statistically invisible, then I wonder who it is laws against polygamy are protecting? Indeed, it might well be the case that the abusive, child-bride instances of polygamy gone wrong are driven even further underground by uniformed officers of the law and the principals they represent.
Can we imagine a world that allows for plural marriage? Or is it so morally offensive that we dare not speak its name?