I think it's more those who sexually fetishize their female character too much that turns some people off. For example, my FC has a few guys who play females. Most of them, it's no big deal. They may dress them in lewd outfits, but it stops there for the most part (though even that has the connotations of reducing women to a sexual object).

One player tends to RP their character a bit too much like a cat girl in heat and is often found over on Balmung ERPing. It can come off as a bit off putting at times as we've had irl female players ignore him or threaten to leave the FC because they feel harrassed by him when he gets into it too much. This can understandably lead to people being creeped out.

Personally, I don't care what people play as long as they're respectful to others.