Tactical issues
Would it matter if acceptance of gay marriage did lead to acceptance of polygamy (either socially or legally)? Should civil marriage be separated from the religious rite of matrimony, with the former being guaranteed by the state regardless of the gender of the two partners? Shouldn't GLBT couples have the same rights as different-sex married couples?
I think what is sometimes forgotten in such arguments (and deliberately ignored by the religious right) is that the prospect of marriage equality is largely academic in most US states (since same-sex unions are for the most part generally illegal already) and therefore not much of a serious threat to the status quo, Massachusetts and Vermont notwithstanding.
On the other hand, the orchestrated right-wing movement to enshrine anti-gay discrimination in every state constitution through amendments that prohibit state recognition of marriage’s ‘legal equivalents’ presents a very clear and present threat to the preservation of previously won GLBT rights. If such amendments continue to pass around the nation, more and more people will lose the parenting, adoption, inheritance and domestic partnership benefits they currently see as secure. The religious right, emboldened by their legislative successes, will not stop at constitutional amendments but will press on to strip further rights and ultimately recriminalize same-sex relationships through whatever means available.
I want to encourage people to stay smart (or get smarter) about what are the real tactical issues of discrimination vs. the important but longer term issues of achieving total civil equality. We have to keep our energies and attention focused on combatting these very real threats (already realized in Ohio at least) while continuing to advocate for the longer term goal of marriage equality. If we don't manage to successfully reframe the present debate in terms of what is at threat should such amendments pass, we might very well convince half the electorate that gays should be allowed to marry and still end up having much of our existing relationship and parenting rights snatched out from under our very noses.