So today we are drawing the line at gender equality, and refusing to consider the rights of any group that has the preference to engage in plural marriage. That's fine with me, because I don't wear my ideologue hat anymore, but as an intellectual exercise it is rather interesting and slightly ironic to witness the ad hoc justifications for denying rights to certain people coming from the mouths of those who probably consider themselves champions of all sorts of special rights.
In all honesty, I can't really think of a rational justification to prevent consenting adults from engaging in plural marriages, as long as the rights of everyone involved are otherwise respected. There are some possible societal implications, since most plural arrangements end up leaving many males out of the procreation game, possibly fueling unrest.