I can understand Andrew Sullivan's passion regarding gay marriage. I for one don't consider the proposition tantamount to the doom of our world as we know it. I'm a little disturbed, however, by his frequent referrences to this being the "civil rights struggle of our time". This and the point that heterosexuals have not exactly maintained the sanctity of the institution are both the other side of the old slippery slope argument. The charge that the first compromise on an issue, for example loosening divorce laws and allowing bi-racial couples to wed, will ultimately result in the entire demolition of the practice was and still is being trotted out. For example, if the requirement of one man one woman were to be removed, then what would stand in the way of polygamous marriage? To say that bigamy won't necessarily follow from gay marriage runs into a hypothetical of if someone said back in the miscegenation days that allowing colors to marry whites might someday lead to men marrying men and somesuch.
Again, my opinion on the issue is to allow anyone who wishes to extend rights over themselves to others to do so as they wish. I'm more concerned with empowering a sloppy rhetorical practice.