it does seem extremist as a perspective, but that extremist might think talking about the franchise is akin to marketing or a more passive or subtle way of the franchise receiving funding.

Probably a better argument is that JK Rowling is not as influential as some anti-trans activists, and our behavior and norms should ideally be rational and reflect those priorities.

I agree with you that coalition building is important, and in this particular case probably more important to trans rights than strict adherence to rules like never speaking of Harry Potter.