Deadnaming a trans person is equivalent to telling them they are not who they say they are. If you deadname a trans woman as some sorta "gotcha" because they disagree with you, even if their rhetoric and actions harm the very community they're a part of, that's not far off from being the type to say "YWNBAW".

Their name is inherently connected to their identity. It's one thing to call Caitlyn some smarmy Trump-esque name like "kookie Caitlyn", or some other feminine name that isn't hers to mock her like "Candace" or "Karen", but in using her birth name/deadname, you are basically telling a trans person that their identity as their gender is invalid, and that they are only seen as the gender they identify with when they agree with you.

Instead of saying "you will never be a woman", it says "you are only a woman when I feel like you deserve to be one".