This is likely not the right thread for a discussion about this, and I suspect it may be purged due to how personal it is, but I would personally argue that you're seen as insincere since you still identify with the ideology you claim to have left. You actively identify as "former anti-SJW," and identifying as a former anything tends to not carry significance unless that person is serving a corrective role: e.g., a former Jehovah's Witness that exposes how the cult works and tries to integrate other former JWs, or potential former JWs, into common society.
Beyond that, here on CFC, you most often publicly agree with the people who hold the views you say you've left behind. Once this happens, yes, people start to insult you. You wear this ideology as a badge despite claiming to no longer be a believer in it. In discussions, you continue to uphold the ideology. When reading other discussions, you agree almost exclusively with people who believe in the ideology. It is very rare that you put forward a position that shows you are anything except the ideology. It is possible you believe something better now, but at least publicly, you don't express this beyond insisting that you've left it all behind. When your views get interrogated or you're given an opportunity to tell us what your beliefs are, you don't tend to stray very far from what you claim isn't you anymore.
I don't agree with your former friend about the time it takes to deprogram prejudice and bias, that gut reaction of rejection and disgust, since this is something anyone serious will say takes a lifetime. I still have moments where I pause and have a reaction from my upbringing, and my cut away from that cult was as clean and definite it could possibly be. But at least as a bystander who watches how you interact on here, if someone asked me what your belief system was, I'm not sure I'd have a different answer than the belief system you say you've rejected.