The National Organization for Marriage has to support bigamy and/or polygamy. It's a logical and foreseeable outcome of their stated goals.
We now live in a country where several states have legalized same-sex marriage, but the Defense of Marriage Act prevents those marriages from being recognized on a federal level. More importantly, those marriages do not have to be recognized by other states, and NOM is fighting tooth and nail to make sure that doesn't change.
Let's be blunt. The right to marry isn't just the right to marry--it's also the right to divorce. We've already seen some same-sex couples who've gotten married legally in states that allow it move to states that don't recognize their marriages, then split up some years later, and access to the courts for divorce has become a dicey issue.
This poses some not-insubstantial legal questions.
For example, are same-sex couples who marry in Massachusetts "divorced" upon moving to Kentucky? Are legally-married same-sex couples who marry in Council Bluffs, Iowa legally divorced upon crossing the Missouri River into Omaha, Nebraska? What if a legally-married same-sex couple moves to a state that doesn't recognize their marriage as valid, but wants to divorce?
On the surface, these questions seem a bit absurd, but it wouldn't seem that they'd automatically lead to problems of bigamy and/or polygamy. But they can.
Let's imagine, for a moment, a pair of young men, in their 20s, who fall in love and marry right after college in Iowa City, Iowa. One of them, Johnny, is gay; the other, Teddy, is bisexual. Let's say they move to Charlotte, North Carolina, where their marriage is not recognized. Let's say they split up, for whatever reason, as many young couples do. They have no access to the divorce courts in North Carolina, as North Carolina doesn't recognize their union, so they just go their separate ways.
Let's say Teddy meets a young woman, Rachel, a couple of years later. They fall in love. They get married in North Carolina. Let's say Teddy gets a sweet job offer in Des Moines, Iowa, and takes it.
See the problem yet?
Teddy's still legally married to Johnny in Iowa. Now he's married to Rachel, too. Even though North Carolina doesn't recognize the first marriage as valid, Iowa recognizes both marriages (as do New York, Washington DC, Massachusetts, etc). Now Teddy is an unwitting (and probably unwilling) bigamist, not due to any deception on his part, but because the law forces him to be.
This is a foreseeable result of DOMA's provision allowing states to ignore same-sex marriages. It makes a complete hash of marriage laws and directly creates nightmarish situations for the courts and for the couples that could get caught up in them.
So I ask the National Organization for Marriage, why do you support bigamy?
[By the way, please don't misconstrue me to be picking on bisexuals here. I'm just using the example because it underscores the problem--I'm not suggesting bisexuals are inherently bigamists, or that they're promiscuous, or serial monogamists, or anything like that. I'm just trying to posit a plausible scenario.]