I think a lot of it stems from the social justice concept of ceding to people who have a marginalized identity in discussions about that identity/community. Like a lot of things, it’s an idea that’s necessary (because of situations like cis men being in charge of making decisions about women’s healthcare policies), but is often taken to an extreme that can’t be sustained because, well, people do have different opinions, and if your policy is to accept whatever someone says as objective truth just because of their identity, then you’re probably not accepting or acknowledging other viewpoints within that community.
I think the same idea has bled over into discussions of shipping. A person’s survivor status is regarded like a credential, but people miss the distinction between respecting someone’s personal feelings and taking them as law.