Maybe? I don't know. I mean, I NEVER really ran into it. Unless I've forgotten a lot of other people's posts (which I'll freely admit is entirely possible), I don't recall many incidences of people on my flist getting hate mail, either, at least not of the "You are sullying our beautiful characters by making them OMG teh gay!!!1!" variety. Maybe you got some with the fic you're talking about because people had an expectation that your fic would be gen/het, so it might depend on the readers' expectations more than the slash?