I ditched a group of mums (secret fb group, met via MN). I was part of a few. 
I found the women cliquey and they always bragged about their wonderful BFing, ignoring the FFing mums, criticising other mums for not having the right baby carrier, or choosing to forward face in a car, allowing your child to wear cruiser shoes before they can run bare foot, spoon feeding, choosing disposables rather than cloth, buying pink for your baby girl rather than use her big brother's hand me downs, chucking your baby in their own room at a few weeks old, not consleeping, not feeding organic - the list is endless!
These groups of women made me feel inadequate, paranoid, self loathing and the irony of it - isolated!!
Stupid thing is, when I left my two groups I was bombarded with messages from some of them who AGREED with my reasons for leaving, empathised yet STILL they chose to stay.
I left after one mum went one step too far and criticised me for 'not doing enough' for a family member and used my home and financial circumstances as a basis for her attack. She apologised but for me it was the last straw.
I realised that in my life I had a wonderful family and a wonderful group of friends and discovered that actually I didn't need them.
Granted some of them have become RL friends but I see it that I already had a life with friends and didn't need to find anymore - I didn't anyways!
A year or so on, I am so much happier that I ditched these 'friends'.
My confidence in myself and my parenting has grown massively, I don't question myself or allow others to look down on me (which some of them did!) and accept that I am doing the best I can!
Some of the women deleted me as a friend on fb as soon as I left the group - which says it all really, and one even BLOCKED me. I didn't say anything untoward or name call; they simply acted with passive aggression IMO. I am friends with a few still and every few months we matter. I dare say if I lived closer I would have arranged a meet up.