Far East: The Slippery Slope Fallacy states that something is wrong only because it may lead to something else that’s bad. In this case, however, people that are against gay marriage are bothered by gay marriage itself to a certain degree, whether it be the “abominable”-ness of the act as clearly stated by the Torah, or the ramifications of gay marriage, such as legally being able to adopt kids, and the propagandization of gay culture into our education system and society.
The fact of the matter is, that under the new all-inclusive definition of marriage that liberals are starting to stick in some states, just about anything goes including incest and bestiality. Supporting gay “marriage” legally, doesn’t “lead to” (as implied by the fallacy) supporting (somehow still immoral things such as) bestiality and incest, it literally changes the definition of what marriage is from a religious ordeal to a legal one. And while you may give reasonable explanations why bestiality will never be legalized, a) I fail to understand why it should be less illegal under redefined marriage laws to marry a sibling than it is to marry the same gender, in fact it’s more natural b) it would not reaffirm you fallacy theory because bestiality and incest do exist. They do not have to be led up to. They just have to be legalized and under current definitions in many states I see it as already legal without a precedent.
So in conclusion, by falsely stating that something true is a fallacy, you have stumbled upon the Fallacy Fallacy, thereby committing the chief fallacious act of the day.