I think to a degree the left pushes people out though, as your lefty card needs to be spotless or it’s revoked.
Sometimes a person can say one thing wrong and they’ll be labelled an alt-right fascist, and not part of “the group” on the left, especially online.
Obviously that doesn’t make people right wing, but it is a problem that pushes people away from more left leaning views/groups. Rather than try to discuss and correct, people will berate and ostracise.