A mix of things really.
Some of these women simply have not thought things through properly and (not unlikely myself a year ago) they genuinely believe that transgender means the same as transsexual...not realizing that the movement has been taken over by a bunch of narcissistic misogynistic wankers.
Some of them will be scared that airing their true views will earn them the same treatment as the woman who took the beating. Rabid support will grant them safety, so to speak.
Some genuinely believe in 'the cause'. Actually believe that men are more discriminated against than women, and that these transwomen need protection from feminists. Who see the whole thing as no different than gay people fighting for their rights. Not seeming to link the dots to realize that the trans movement is homophobic...and that sexuality in itself is 'transphobic' :S Unwilling to read the numerous accounts of lesbians who have been pressured into sex with male bodied people as its 'transphobic' to say no. Or unwilling to care until it affects males on such a scale (which is unlikely to ever happen as female people don't tend to believe they are entitled to sex with anyone..and I can't see many trying to pressure male people)
Most of the above, will eventually have a moment where they do stop to think a little deeper, and thats usually when one turns gender critical.
Being GC is made out to be some horrific crime, but the huge majority of people I know who are GC would stand alongside transgender people in fighting for their own spaces and such. Just they do not agree that females should be thrown under the bus in the manner that TAs are fighting for right now. And this is why the threats of violence/rape and actual carrying out of these acts happens. TAs tend to be total misogynists, who are obviously not going to be impressed by women standing up for themselves. 'Genuine transsexual people' are just as scared of these violent men as females are, and as such stay well away from anything to do with the whole movement, or are threatened in the same manner themselves.
This in turn, makes it appear that trans as a group are violent bullies. Each incident makes more people wake up. Which makes TAs more violent..and so the cycle continues.
Its all so sad really. Both females and transsexual people are being thrown under the bus...and so many still don't see this. Self identification is bad news for both females and 'normal trans' alike. The only people it will benefit are predators. Genuinely think that by the time this understanding is 'got' by enough people, we will be to far down the rabbit hole to turn back. And thats fucking terrifying.
Probably waffling a bit now, but this topic is so depressing. It really upsets me how I did not see how anti-female and homophobic the whole thing was until fairly recently, and how I probably indirectly joined in with the silencing of lesbians and such...