If by "red" states you mean states that went for Bush, I can name a number where the margins were close enough that the outcome next time will be different if the GOP nominee is someone who makes social conservatives stay home. Start with Ohio. Bush squeaked by last time - and it was on the strength of a no-gay-marriage amendment that brought out the social conservative vote. IF the GOP is running a candidate who believes in "gay marriage", you can say goodbye to those social conservatives, or at least to enough of them that the state could very easily go "Blue."
Of course, political calculations aren't the only reason I fear the nomination of Rudy. My concern about the future of our civilization - western civilization - is an even bigger reason. Homosexual marriage - which he supports, apparantently - would be the sign of a final downward spiral, by destroying the insitution on which civilization rests and by elevating perverted behavior to the status of normality. You don't have to be a fundamentalist anything (I'm not), to understand that -- and enough voters understand it that Rudy's gay agenda will sink his candidacy (and the GOP if it nominates him).
Homosexual marriage - which he supports, apparantently ......
At every speach he gives Rudy has come out AGAINST gay marrage.