The "homeless" analogy fails, because the Meetup isn't a city; it's an optional event run by volunteers. They don't owe a particular asshole membership, and they harmed the very group by allowing him to stay.
If we do want to try to stretch the analogy, with the meetup-as-a-social-gathering being our city, then the asshole was breaking one of the city's ordinances - a social rule of not being an asshole who harasses others. Homeless and homeful alike would be arrested and fined, or put in jail, if they flung bricks through the windows; someone who's breaking social norms and making others feel unsafe ought to be expelled from the group.
Not defending this person, of course - just offering a wider perspective. I'd certainly pull this person aside frequently - if the group allowed for it constantly rather than shaming the person then I'd immediately look to leave the (now toxic) group if I couldn't convince them of the danger.
A meetup is a social event, and as such it has social rules, which are the equivalent of laws here. Making people feel unsafe and being an asshole is breaking those social rules.
A city can fine people or put them in jail; a meetup can forbid people from attending.
One key problem with this analogy is that everyone has to live somewhere, even the homeless. But not everyone needs to go to a special interest meetup. The organizers of the meetup didn't owe more to this one asshole than they did to the group, yet they made the entire group pay the cost of interacting with him.
As communities we deal with situations like this all the time. That's why we put criminals into jail, for forcibly separate them from the community at large (the nation) because they are actively causing problems (and to punish them), and it's not feasible to exile them anymore.