I think it is difficult for people when they buy wholeheartedly into the ideology without thinking through the implications, and then end up trying to defend it.They've been fully stonewall-trained and told what they must think, and often IMO do believe it because they swallow the idea that being trans is just like being gay – you're born that way, you have a right to exist as your true self, and the true self of a TW is being a woman, just as the true self of a gay person (as was, in the era when gay rights were won) is being same sex attracted, and that cannot be erased or denied.
It takes a long path of thought from that point to realising that unlike being gay, genderism makes no rational sense when logically analysed. So people are stuck in that mindset and will say anything to try to explain it, making them come out with all kinds of breathtaking statements. When you really think about it it's horrifying, but people are not really thinking about it. (Well they are in increasing numbers, but in the meantime we get this kind of thing.)
It's helpful in some ways, in exposing the unviability of it all.