I joined a couple of these groups because I was fed up being "the weirdo" who used slings rather than prams, cloth nappies, and breastfed and coslept.
The fact that I did all of the above (apart from cloth nappies - that was just being cheapskate
to deal with my nightmare, never sleeping, never able to put down DD - was neither here nor there - a lot of people on these groups also fell into a "style" of parenting just to cope with their rather difficult babies.
And even now it is quite nice to have somewhere to talk about how to deal with requests to breastfeed a toddler when out and about, or how often they still feed at night etc without being made to feel a weirdo again.
Generally I find them supportive, and most people are nice (I avoid the ones where people call each other "mama" - makes my teeth itch! 
But yes, there are some people who are a bit "committed" to it all ideologically, and sound a bit nuts about it all. So you just ignore them eh? 
Although I love a good argument about how quacky homeopathy is, and that vaccination is actually a good thing etc. Oh and yes I DO praise my child, and say "good girl" etc. And I was the one rugby-ball carrying my tantrumming 2 yo away from the swing park this afternoon.... just because I like to be a gentle parent doesn't mean that I don't enforce boundaries (like we need to go NOW) 