Would Plural Marriage Be On the Heels of Gay Marriage?

A popular and, to my thinking, convincing argument against unmooring the definition of marriage from the traditional/historical "one man, one woman" construct is that, once so unmoored, there would be no stopping point. That is, if the alternative view, that "love is love," is taken seriously, then there would be no reason that the numerical restriction should any longer be taken seriously, and plural marriages would be on the table.

I came across this article in which a Mormon mucky-muck agrees, and suggests that a win for gay marriage would result in new lawsuits bringing polygamy and embarrassing Mormon doctrine and history into the limelight. In particular:

Should any state succeed in allowing homosexual, same-sex marriages to become law, it is almost certain that polygamy will rush in on its heels. Should same-sex marriages become legal, there will be no moral high ground for the court to take. I can assure you that it will not be long before petitions come before our lawmakers demanding similar recognition for plural marriages.

It is important to note that, if we eventually recognize gay marriage, it must be done through the political process, not the courts. Through the political process, we can simply declare that the sensibilities and culture of the people dictate that marriage include...whathaveyou. If we opt for a shortcut through the courts, we will be forced to follow that wormhole through to its logical conclusion. In other words, the court-route would require the court to declare, by fiat, a principle by which marriage would be defined. If that principle is something amorphous like "a committed and loving relationship," as the pro-gay marriage folks would have it, then there is absolutely no reason why such a principle would not extend to any such relationship, regardless of number. Being thus tethered to principle, rather than to the sensibility of the people, there would be no stopping point, and plural marriage must also be recognized as a matter of judicial and logical consistency.