What do you mean by "whining"? About their personal lives (job, family, health), perceived persecution ("it's because I'm Pagan", "Those Christians are so oppressive"), cattiness ("That other coven sucks because they don't do it like we do it")?
I think that regardless of the reason for the group, like attracts like. People who are looking for a place to hold a b*tchfest and complain about the world in general and how much it sucks and how much they're put upon will end up hanging out with people who will not only let them, but will agree with them and validate their feelings. It feeds on itself.
If a bitcher ends up in a group that doesn't put up with it, they will usually not last too long, because the rest of the group just doesn't want to deal with the drama llama, and they will eventually move on to find a group who will let them witch and moan and validate them.
If you aren't finding what you need in a given group, move on - you don't need to be sucked down by the well of negativity if it's not where you belong and not the energy that you mesh with. Just my $0.02.