If someone signs up for Caravan and wants to participate, but is told by a party leader "We're not inviting you", then I've got no problem with them doing whatever. They're trying to get involved but being denied by someone else who's basically being an idiot. The issue is when someone signs up and then runs off without even attempting to get involved.

Ideally, the individual in question will try and find ways to help out anyway. But that isn't always feasible.