The reason I think this is that I suspect most of those who are firmly against it don't know or understand the arguments for it or they are using "moral realism" in a way that is different from how philosophers use it.

This is pretty likely. I spent about a minute trying to determine what the words were actually supposed to mean, then decided that it was pointless, gave up, and refrained from voting on that question. (I did this for a few questions, though I did vote on some, then gave up on the poll.)