It's possible that people can actually be former leftists/socialists/communists/etc and have "left the left" so to speak. I've been noticing here that the common response to this will be "they were never really leftists/socialists/etc. anyways" or "they were never really serious to begin with." It's possible that it could be the case, or maybe they actually were on the left, but they just didn't have the stomach for the real shit I guess.
I think we shouldn't be too quick to jump to using the "no true scotsman" fallacy in these cases. For those who don't know, it's basically saying "you weren't REALLY a leftist, cuz otherwise you never would have left." The same argument is used by religious people when someone leaves the faith: "oh they were never a REAL christian, otherwise they wouldn't have become atheist/agnostic."
To give some concrete examples, take Eldridge Cleaver. He actually was a Black Panther, radical, communist, etc. but then later in life became a Reagan conservative. Or Angela Davis. She actually was a radical but now she tells people to vote for Biden.
TL;DR: People can and do change, sometimes for the better, sometimes for the worse.
Having to argue for trans rights from the closet has made me the perfect trans ally, I think, precisely because I have to come up with reasons to be deeply invested in trans issues without outing myself. So even if I suddenly start identifying as a man again, and lose all empathy for my fellow human being... Well, I can't exactly un-analyze the connection between trans issues and men's issues, autistic issues, and class struggle.
I guess we can see it as three redundancies: Are you directly affected by this form of marginalization? -> If not, do you feel empathy for your fellow human being? -> If not, how are you indirectly affected by this issue?
The problem is that empathy for the marginalized often comes from one's own experiences with marginalization, and that it often takes that initial empathy to be able to develop a deeper understanding of how one is affected by a given issue.