I think it's a pretty logical assumption that a transwoman has male physiology, and whilst there may be aspects of a transwoman that are more feminine, they aren't completely immune to male traits.
Given that, it's not wrong to assert that there's a greater likelihood of violent behaviour. It's not a personal statement, but a class one.
The problem lies in the fact that a transwoman wants to be classed as a woman, and therefore to argue they are male (or part male) seems to offend some. Maybe a better way to express it is that although they are female (for the sake of argument), they evidently have a male physiology which is a result of male biology, ergo they at least inherit some male traits along the way, one of which is a higher tendency to be violent). However you express it, it's a fair statement, but it won't be warmly received.
In truth, it's not usually warmly received by anybody. We don't like to be treated as a 'class', especially when in the context of a negative attribute (violence for instance).
Sometimes, I think if David Attenborough was documenting us, we'd have no problem accepting that men and women have certain predispositions, and of course there's huge overlap, but there are differences 'on the whole'. We just seem to want to bury our heads in the sand or take it all too personally.