I mean it’s pretty straightforward - due to trauma over her past experiences with sexual assault at the hands of cis men, she now sees trans women as a facade used by predatory cis men to sexually assault cis women in bathrooms and locker rooms and other segregated spaces.

To her, trans women are really cis men pretending to be women, to make it easier to rape them. There’s kind of no nice way of saying it.

It’s textbook transphobia / queer bashing. Fear of sexual assault at the hands of queer people is probably one of the most basic reasons to justify this particular brand of bigotry. “I don’t hate queers, I’m just concerned for the safety of -“ take your pick - women, children, sometimes even men. For JK it’s women.

She deals exclusively in dogwhistles.

Using a dogwhistle instead of more well-known hate speech does not mean a person is innocent of bigotry - quite the opposite.

This is something she wrote on Twitter... JK Rowling wrote, "There are no trans kids. No child is 'born in the wrong body'. There are only adults like you, prepared to sacrifice the health of minors to bolster your belief in an ideology that ends up wrecking more harm than lobotomies and false memory syndrome combined."

Just because you agree with them doesn't make them not anti-trans - it just means you agree with anti-trans things.