I think the childfree movement is anything but anti-feminist. As far as I can see it is about people supporting each other in a lifestyle choice that is incredibly unpopular in mainstream society.
I think the majority of people allied with childfree groups are women as they are the people most stigmatised by their choice so possibly need the most validation. Women who openly don't want children are often regarded with disgust/contempt/curiosity or suspicion (often much, much more so than men), as demonstrated by some of the attitudes on here, so it makes sense they find support with a 'movement', much like feminists, eh?
The expectation that all women should have or want children is a huge feminist issue and challenging the notion that all women are maternal (and the expectations of care/drudgery that go with it) is definately NOT anti-feminist.
Some of the language referenced here is pretty disgusting but unless you've questioned every childfree person to check whether they approve/use such language it's a case of tarring everyone with the same brush. I would also add that a lot of criticism is levelled at mothers by the childfree, not because they are misogynists but because 9/10 times it will a mother, rather than a father who is 'letting' her child run around Tesco or screech in a cafe so rather than hating mothers specifically it may be they are hating the attending parent which will most likely be a women as the fathers are doing "more important" things
That women are primary carers is another feminist issue raised, but not caused by, the childfree forums.
Before you ask, I'm not saying all this as a childfree person, I'm 8months pg
but I recognise it is hard living in a society where 95% of the population will take their lives in a very different direction from yours and it's anything but 'mentally ill' to want to contact the few who feel the same as you and who are sick of things like parents leaving work early to watch kid's plays and babies and toddlers in pubs etc.
I'm sure all ^ will get picked apart but I think my main point is that while some childfree individuals may be hate-filled and misogynistic, the movement as a whole seems to me to be support for people, especially women, going against the grain and that is anything but anti-feminst.
But anyone who calls my baby a cunt-maggot will get poked in the eye...