"But I'm not sure I see how the lack of realism could cause harm to the majority of femslashers who are queer and female. Confuse them about their own experiences? "

It might insult their own experiences. Which, I think, is really the objection that most of the gay men have, who are objecting to slash right now. When one's identity is involved, it's difficult to tell the difference between an insult and an injury...

Now that someone has mentioned it, I realise that I have never written a cat into any of my dyke fics. Hmm!