Yes - gay marriage does threaten some marriages

Here's the thing. Gay marriage is not a threat to marriage, per se. But it is a threat to some marriages. Those people who are in mixed marriages - one hetero, the other homo - will have their marriages threatened, especially when one of the partners has been living in silence about their orientation. So the religious right - that's so often wrong - do have it almost right. But not in a way that they can say.

The religious right and similar bigots are so set on having reality their way - instead of accepting reality for what it is - that they can't make their best argument for why their marriages are threatened by marriages between two people of the same gender.

Marriages like those of my parents - where both people have a mutual sexual attraction (and are attracted to each other for many other reasons) - are not going to be troubled by the marriages of other people. But marriages that were to get married in order to be respectable, in order to do the right thing, in order to hide desires that one didn't want to admit are going to be in trouble. And rightly so. If one or the other partner doesn't go into the marriage in honesty, then the honesty of other marriages will be threatening.