I draw the line at if you can make a logical argument, there are many logical arguments for not eating meat. There are no convincing logical arguments for opposing gay marriage that don't involve bringing mystical wizardry into play.
Except you can't assume you're right and use that as the basis of an argument against someone who you thinks you're wrong. You'll get nowhere with that. It's the same thing your opponent does too.
It always bothers me when listening to (or reading) a debate and both sides say that the other side isn't being logical. Well, you can't both be logical and still be in contradiction with each other.
