The Left ruthlessly enforces friend/enemy distinction.
These former leftists supported the Enemy on just one issue, and that was enough to get them expelled from the Friend Coalition.
And as you point out, the Friend Coalition and Enemy Coalition is constantly changing.
Fifteen years ago no-one demanded that everyone believe that men wearing dresses were “really” men. Now, refusing to pretend that they are gets one expelled from the Friend Coalition.
Same with Israel. In order to remain in the Left Friend Coalition they have to support Hamas against Israel.
That isn’t just on the left.
If you said on this site that you didn’t agree with the patriot act, or the Iraq war, you were banned. Now it’s the complete opposite. Just two examples.