In other words, do I believe in majority rule? Sure, if we ever get to the point where enough Amercians want to marry their cars, I guess they can change the law to do so. Just don't make me pay alimony to my 1976 Gremlin, OK?
Seriously, something happened to homosexuals in this country in the last twenty or so years. They saw a lot of their own die from AIDS, and had to deal with the problems of hospital visitation, and hostile relatives upon death. Lesbians acquired children through artificial insemination, and have to deal with the problems of being parents. These problems were never faced by goat humpers, car worshippers, or one-night-stand threesomes. The respect that our society accords marriage has become appealing to some of them. Enough people know, or are at least acquainted with someone in a committed gay relationship to empathize with them. I don't know anybody who really is suffering because they can't marry their Mazda.
We CAN, as a society, draw distinctions between expressions of sexuality that are permitted, and those that are discouraged. We always have. It's just that there are enough people out there ready to think about moving the line on this particular facet. Is it possible to happen with other things in the future? Sure, anything is possible, but essentially all of what you fear down the slippery slope will have to overcome a crushing burden of convincing 90-99% of the people who are dead set against these acts.
I don't. I believe in a free republic. This is not a socialist country based on mob rule.
If homosexuals marry, the law says equal protection. To not allow other fetishes their right to marry would be discrimination based on how they choose to have sex (with whatever).
If we allow one dysfunctional sex fetish to be called marriage, we must do so for them all, no matter how small their number.