He’s a writer. If he wanted to support her right to speak, but disagreed with the content, he could easily have made that clear.
Even if he only wanted to support her right to speak, and realised it was being misconstrued, he could have explained that without much difficulty, and been apologetic.
Instead, he behaved like an abusive man: he offered apparent support, then responded to an openly abusive tweet with a lazy mantra that is in direct conflict with all that she’s been saying.
But the worst thing about all this, is that in all the furore and abuse, the quiet, thoughful words that JK Rowling wrote have been overshadowed. This was her moment, and he fucked it up royally.