I'm with you, but understanding someone's view sometimes means acknowledging that it is, in fact, irrational. There are reasons some give as to why they think that cis women need protection from trans women, but those reasons are either not rational since the vast majority of evidence is to the contrary, or they are founded on the extreme minority of evidence that confirms them (meaning the search for evidence was conducted irrationally).

If I try to understand someone's point of view, restate it to them in a way they accept, and present overwhelming evidence to the contrary, and their response is to say the evidence is irrelevant because it's possible some of it was biased, that's irrational.