I don't think the issue is with having an opinion, but rather with putting words in someone's mouth the second they mention their own opinion. There's a difference between
A: I like X/Y. B: Oh, I don't like X/Y.
and
A: I like X/Y. B: Well, that's okay as long as you don't romanticize it or write fic where X is a homoromantic demisexual barista who serves coffee to panplatonic bisexual med student Y because then X is subservient to Y and that's gross tbh.
no subject
A: I like X/Y.
B: Oh, I don't like X/Y.
and
A: I like X/Y.
B: Well, that's okay as long as you don't romanticize it or write fic where X is a homoromantic demisexual barista who serves coffee to panplatonic bisexual med student Y because then X is subservient to Y and that's gross tbh.