I was the last one to incite a debate about Hasan on this site, and this was the comment that reframed my thinking positively.
Open arms no, but if they're willing to kill fascists then I'm open to some sort of reeducation/service to prove loyalty.
Like seriously, if someone's willing to kill for left principles after changing, I would be open to allying, but with the caveat they're on a short fucking leash. Put the Battle Royale collar on them until the dictatorship of the proletariat is established.
I should say I'm only half-jokint about the BR collar. Some form of discipline/surveillance must be done with former centrists/liberals in the coalition who might turn reactionary so that they don't go and hijack the movement.
They can join as junior (controlled) partners. What this looks like in an electoralist context I honestly don't know unless you have union power substantially higher than it is.