Because most bullies do so because the object of their harassment is violating scripture. In fact some of the people who bullied me as a child carried around bibles with them to point out the specific passages I was violating by being shy and having poor fashion sense. I'm sure their parents spent a lot of time at the dinner table every night telling them why they should hate shy people for being subhuman, and their preachers shouted it from the pulpit ever Sunday. Damn Christians and their making people like me into subjects of daily mockery and harassment.

Oh wait, I was bullied because I was different and thus seemed weird to other kids. You know, kinda like how gay kids are different, both in their nature (who they are attracted to) and in their behavior (in some cases). Thus, they have big targets hung on them for bullies. Just like kids like me did, or kids with big ears that stick out, or fat kids or any number of other kids.

Kids are a tough crowd. Even if a preacher or their parents don't tell them something is bad, heck, even if said preacher/parents tell them that such a thing is NOT bad and to be nice, most of the time they'll sniff it out anyway and mock it as they see fit. Kids can be nasty shits.

But no, being against a particular legal issue means that you see gays as subhumans, which means that you will pass those beliefs onto your kids and turn them into little klansmen, which means that your kids will become merciless bullies, which means that they will drive gay kids to kill themselves. If you are against gay marriage, you are causing the deaths of gay kids. Fact.

Sound like the kind of argument that, if used by the other side, would have people shouting "Slippery Slope Fallacy," and dismissing it immediatelly.