It's already happening
Mark Steyn says "I told you so" as the forces of unreason come out of the woodwork with Phil Robertson non sequiturs.
A while back, a well-known liberal columnist dismissed the argument that to compare heterosexual marriage on one hand and same-sex "marriage" on the other was to compare apples and oranges as "an obsession with fruit." I suppose if you're determined to avoid the central problem with same-sex "marriage," refusing to engage the issue in the first place is as good a way of doing so as the other emotional and illogical arguments the Left uses for that purpose- and with which, in a modern society far more adept at emoting than at logic, it seems to be succeeding.
But the issue involved in the civil rights movement of the '60's and today's one-sided debate (you get silenced if you're on the "wrong" side of it) concerning homosexuality isn't even close to being the same- not that the hate-filled folks who are so quick to falsely accuse those who disagree with them of being haters and bigots particularly care. even if this is a revelation to some people, being African-American, for example, is a thing you are. So, admittedly, is being homosexual.
To hate people for being black or homosexual would be bigotry. The problem, though, is that hate, for the most part, isn't the issue, no matter how badly the Left would like to pretend otherwise.
Being homosexual isn't the controversial issue. The ethics and social standing of homosexual behavior is the issue. The moral- and social- objection to same-sex "marriage" and the general equation of homosexual and heterosexual relationships is not to an ontological condition like being black. It's to behavior which Western society, for good reason, has traditionally regarded as immoral, and the treatment of that behavior as the equivalent of the foundational relationship of human society. Nor is it even about preventing people from engaging in that behavior, if they so choose.
It's about drawing a false analogy between it on one hand, and traditional marriage on the other- and merrily falsifying the evidence about what research has told us about the instability of gay and lesbian relationships and the small place monogamy has among gay men on the other. Time after time flawed studies with small samples have been cited as the definitive word on these matters, while larger and less seriously flawed studies have been shouted down in a desperate attempt to disqualify them and claim the high scientific ground.
With a logical fallacy like that at the heart of their argument, is it any surprise that the homosexualists spend so much time calling people names? Nobody seems to notice that there is a great deal more hate being spewed from the Left on this issue than from the supposedly bigoted Right.
You know. The bigoted Right which has a problem with certain behavior.