When people get offended on behalf of others, especially when their stupidity harms the people they claim to be offended for.
Case in point, the Hogwarts Legacy situation. It made trans people look unhinged by association, even though the seemingly vast majority of them were cis progressives.
And if I as a trans person mention how I don't feel represented and don't appreciate what they are doing? Suddenly I'm a Russian troll or something. So stupid.
I think you make a good point that over reacting to perceived offenses can make the "victims" look bad, but the idea that only those who identify as the victim have any right to speak on it is nonsense. I'm a white person but I'm going to call out racism when I see it because to my view of a just society, that racism cannot be allowed. I have nobody in my life that is trans and the current right wing war against trans people doesn't affect me at all, but I'm still going to be an ally and stand against it.
And honestly anyone who blamed trans people for the harry potter game backlash likely wasn't a fan of trans people to begin with. I wouldn't worry so much about their opinion.