Thread incoming.
Alt-Right types don't simply siphon members over to Stormfront, they try to shift the entire community Rightward.
People in these communities have no pre-existing relationship with each other.
In protest movements, there's always the knowledge that, quite likely, someone at the meeting is a cop.
And cops don't simply report what they hear, they stir up infighting.
In online spaces, you have to wonder if you've got Alt-Right sock puppets doing the same.
Who's the cop? Almost certainly that guy no one knows.
If your forum starts radicalizing, you will either tolerate it to maintain access to your community, or you will leave.
So conservatives would be less likely to leave a community that shifts Left, wouldn't they?
Please challenge/elaborate if you have more information.