First of all, if you have skin in the game then it becomes even more important to try to understand the opposition's arguments in order to convince them to join your cause and to prevent others from joining the other side.
As for your example, I am convinced that trans people have a battle to fight for greater acceptance in most (all?) societies. But I would still insist that they have only earned the right to call someone, or something, trans-exclusionary, if they have given careful thought to the argumentation and the positions actually taken.
Sometimes this is easy: if someone says "trans women are not women" then in my mind that is not even a coherent position (define "woman"). But if someone says "most trans women have not had the same childhood experiences as cis women" then that is (to me at least) a statement of fact. Calling the latter statement trans-exclusionary is not what I would call a well-reasoned opinion.