It’s mentioned in the LNs that fellow 86ers hated Shin because he was pretty much the embodiment of death. If the Reaper joined your squad, it was basically a sign ya’ll are dying. Some committing suicide when they resonated with him, or never resonating again after connecting, forgoing Shin’s protection and dying regardless. The only other one being able to survive being Raiden.
Furthermore, he was also discriminated because of his hair and eye colour. It was evident he possessed blood of the old Empire’s nobility; the ones that created the Legion. All in all, Shin truly believes the reason his parents, brother and comrades die is because of him. And that’s just a very deep hole of survivors guilt one can’t simply climb out of easily.