As I argued earlier, if we look at exactly what it is that Christians promise one another when they marry, it is pretty easy to see why bestiality is wholly incompatible with Christian marriage. In short, a dog not only cannot marry a man, but it literally cannot even vow to do so.
I would argue the same thing can be said of polygamists. Let’s start with an easy exa mple. We have all heard of the biblical King Solomon and his 700 wives (and if not, see 1 Kings 11:1-3). It's relatively easy for us to imagine Solomon having sex with all of them (though not, perhaps, all at once). We can even imagine that he had some sort of genuine intimacy and affection for them (though I myself probably would not have been able to remember all of their names, let alone their birthdates, favorite foods, and so forth).
But however wise Solomon may have been, he was still a finite creature bound by the limits of time and space. As such, it would have been impossible for him to give each of his 700 wives the kind of sustained care and attention that is envisioned in the Christian wedding vows. Indeed, Solomon could not have done something as simple as asking each of them how she was doing on a daily basis. At least not if the conversation was to last longer than a minute or two. There are, after all, only 1440 minutes in a day.
But Solomon is an easy example. What about three people who say they are in love? And – just to make sure we're not allowing our feminist sensibilities to cloud our judgment – what if the three happen to be women?
Again, it's easy to imagine them having sex and perhaps even sharing mutual feelings of romantic and erotic love. But could they all three fulfill for one another, over the course of a lifetime, the rigid demands of the church’s wedding vows? I doubt it. To have and hold another person, to love and cherish that person, and to do all this regardless of circumstance requires a genuine willingness to submit to that person (cf. Eph. 5:21).
But “[n]o one can serve two masters; for either he will hate the one and love the other, or he will be devoted to the one and despise the other” (Matt. 6:24). And that, I would argue, is why polyamarous relationships will inevitably fail from a Christian standpoint. Sooner or later – and probably on a daily basis – at least two of the lovers will make valid but competing demands on the third, requiring the third to choose between the two. And the moment she does so, she will be breaking her vow to the other. And because these kinds of conflicts are both foreseeable and inevitable, three or more persons cannot truthfully vow to join their lives together in Christian marriage.
Or so it seems to me. But, then again, I have never actually met anyone involved in a polyamarous relationship. I doubt Rick Santorum or most traditionalists have either. And that really is the fatal flaw of the so-called polygamy/bestiality challenge to same-sex marriage. If someday I fall in love with another man and ask my family, friends, and church to bless our union, I expect and hope their response will be based on an honest assessment of the quality of our relationship – including our willingness and ability to make the Christian wedding vows and faithfully carry them out – not on the unknown and unknowable short-comings of hypothetical polygamists and man-dog couples.
I will even go further and insist that genuine Christian love, agape, requires exactly this kind of individualized response. When, for example, a young man asks his girlfriend’s father for his daughter’s hand in marriage, no one would begrudge that father if he had honest objections because, say, he felt the couple were too young and too caught up in the throes of first love to make a rational decision. But what if the father said: “Yes, you say you love my daughter and promise to treat her well and make her happy. And, thus far, you appear to have done so. But I still refuse to give my blessing because, by that logic, I might as well as let her marry her best friend Cindy or even her cat Socks”? In the real world, if any father did say that, we wouldn't bother with pointing out the flaws of his logic. We would be urging him to see the next available psychiatrist.
The challenge of the gay rights movement is to show our loved ones why Rick Santorum’s polygamy/bestiality argument against same-sex marriage ought to elicit exactly the same response from them.