They feel unsafe because of the ideas that are being spoken (you can’t change sex, you are not really a woman etc). Their fragile mental construction of the world (in which men can really be women in some mysterious way) cannot cope with the presence of other ideas - if it is accepted that you can’t actually change sex, that whole worldview has to collapse.
So I think they are “terrified” of hearing anything said or written that challenges their beliefs because they know they are not rooted in material reality.
It probably is psychologically terrifying to encounter an idea or fact that shakes the foundation of your belief system, or voices things you know to be true but are keeping hidden from yourself.
They then express this as being “terrified” of the person who is saying those things, when that person is no possible physical threat to them, and so they seem ridiculous.
Their real fear is of hearing things they know to be true.