J.K. Rowling is right to be angry. What these people did deserves severe condemnation, as it predictably led to death threats. I've dealt with death threats myself, and it is no joke.
I think some of Rowling's statements about transgender issues are wrong, while others make some sense. But it doesn't matter. Death threats and "doxxing" that facilitates them are not an appropriate way to address whatever you think may be flawed in her statements. If we condemn such behavior when right-wingers do it, the same applies to left-wingers who engage in the same types of activities.
There is the illiberal left, and the illiberal right... and as a guy who loves intellectual freedom, I find it enormously depressing.