Things that made the penny drop with DH.
Showing him a bunch of homophobic tweets and how widespread it was.
Pointing out he could declare he was a woman at the drop of a hat and there was nothing anyone could do (think of the idea of a stag do, where they all decide the are ladies for the day, so stroll into the changing rooms somewhere for the shits and giggles, and you are 'transphobic' for questioning). Then the next day he could be a full on man again. Its not about trans people, its about men who will exploit it.
Surgery or hormones are not required at all. I think this is one if the big misconceptions.
And the concept of medical consent and how this would go out if the window. With implications particularly for children.