I am trying, but I literally cannot think of a way to be more direct here.

The transphobe's hypocrisy is being used here as evidence of their lack of sincerity. i.e., they're conning people. They are conmen. Liars and cheats who believe whatever they have to to convince people to hate the gays too. They will constantly contradict themselves because they don't care about consistency. The irrational fear that they feel is the only consistent position they hold. And so, they don't care about children's causes because they aren't motivated by children's causes.

I know that you already know this; I'm not trying to be condescending. What I think is that you are, like, debate-tricking yourself into disagreeing with something really easily understood by most people.