For me I don't like any group that's main past time is attacking people. Especially when its a case of quoting poeple who aren't part of the group and basically laughing behind their back. Or, as a lot of groups seem to do, hunting out especially dumb/extreme examples from the opposite side and using them to tarnish the entire group. I've seen abortion and pro life groups do that a lot, and athiest ones are quite prone to it too.
Completely off tpic but the other issue I have is people who spread that sort of hate and its unnecessary. I've used the example of abortion groups before on this but its the easiest one to use: I see abortion groups repeatedly find really dumb pro lifers quotes, post them up, and then everyone has a chuckle ripping them and feeling superior. My problem with that is its pointless and just getting fun out of hate. I've seen pro gay groups do it to some extent as well, but I kind of get it more then because they're actively trying to gain support for a cause. Abortion's legal. There's no real fight to be had there in most countries so stirring up hate serves no purpose. And if there IS a fight to be had then the groups aren't doing anything to help. They're closed groups that you only join if you already agree with them or if you want to troll them. They're not having disucssion to try and change people's minds, they're preaching to the choir. Instead of that they could be engaging in civil debate with the other side, or organising events or sometihng depending on the cause. If you're passionate about a subject there's more productive ways to express it than back slapping.
Plus its comparitively inneffective. You can get someone in a tizzy about something but they'll quickly perk up and move on. Hate and anger alone aren't enough to cause change, you need hope. The "It gets better" group in my sig is an awesome charity for helping young gay people feel okay about being gay and get support for coming out. Their fb group could post up the many stories about young gay people being bullied or attacked and try to stir up enough anger to make people want to support change. Instead they post up success stories from people who maybe had a rough start but are now doing well. Those happy stories create hope instead and are a much more powerful force for catalyzing change.
I have gone way way off on a tangent but that's my personal problem with childfree groups. Obviously it extends to any parent group who rips into people for choosing to be childfree as well.
A group patting themselves on the back for being happy doesn't seem as bad to me. We do it on this forum quite a lot, expressing happiness and solidarity over a hobby we all enjoy. Its not as destructive as if we were an offtopic only forum who spent all our time ripping into tma guys if that makes sense?