*gingerly sticking my toe into the fray*
I am feel incredibly blessed that I found MDC BEFORE ttc. If I hadn't, I feel certain I would have 1) gotten every test in the book when pregnant, under the exclusive care of an OB 2) expected to get any and all interventions during labor and maybe wanted a voluntary c-section 3) vaxed and circed w/o even questioning those decisions 4) attempted to breastfeed, certainly, but not with the dogged determination that I plan to approach it now Etc.
My point is: not everyone has the benefit of researching these things before having a child. In an ideal world, this would not be the case. But the mainsteam IS mainstream--it is what most people know. More than that, most people don't even know that there is more to know--i.e., that research into these things is actually necessary. I think many people truly believe they are doing the best for their children, even when they make choices that many of us wouldn't agree with.
That said, I respect the OPs right to vent (and I notice we haven't seen hide or tail of her since that original post, which suggests to me that she's been scared off), if not her apparently public distaste for the mother at her group. To me the helpful response would have been to invite the mother to bring her baby to the next group and to point out that she had a fantastic resource she could draw on if she felt overwhelmed or confused by her new role--a room full of experienced parents. That's just my opinion.
My sister has made many parenting choices that I personally disagree with. On the other hand, I know she is a loving mother who really feels like she is doing the best she can for her dd, and I expect her to have a wonderful relationship with her dd. So, yes, privately I might judge her a little--I can't help the way I feel. But I would never make her feel guilty about her choices (she knows that sometimes her choices are not ideal, but the best of several imperfect options) or accuse her of being a bad mom. I am not in her shoes--I don't know what it's like to negotiate her particular set of responsibilities and problems. If I felt I had something to offer that might help her, I would volunteer information--if I had known more about bf when her dd was weaned, for instance. But I don't think angry judging of anyone--the OP, the mother at her group, the posters who objected to the original post, my sister--is particularly helpful.