I've just read the article here .
I think the link to educational advantage of NCT is misleading. The article is really claiming that the perceived educational benefits (see middle paragraph) are generated by the behaviour and mindset of a particular type of peer network (middle class parents), but that NCT is promoting or entrenching this because the network is really the key benefit that most people get from NCT. It implies that if you can't afford NCT you won't have access to this network and therefore your children could be at an educational disadvantage from birth, but this shouldn't be the ethos of a "national" charity which only subsidises a fraction of placements and as a consequence of cost is only available to those who can afford it. Basically you're buying your friends.
The concept of antenatal peer groups has been around for decades and in itself is not limited to middle classes. Plenty of courses are provided on the NHS and through local organisations but it's true NCT has found itself occupying a very specific demographic space. I think that even without NCT many people in this demographic would be inclined to form their own peer groups and the same behaviours wouls result.
The point would be better made if the author had written the article from the point of view of a national charity having the responsibility to bridge a class gap through shared experiences of events such as childbirth. I think this would be a point well made but you would still see groups or sub-groups being formed between people who felt they had commonality between them for whatever reason. Think baby classes - anyone can attend them, but you mostly tend to develop and foster friendships with people you identify with.
Frankly the success of your group depends on its members though as it does with any. I'm definitely one of the middle class parent types that the author refers to but I would have been looking into "development, local educational opportunities, kids books and exercises" regardless of NCT. I just found it was (mostly) nice to have a like minded group of people to talk about that with and I would have found them somewhere else if it hadn't been for NCT. I also enjoy the same conversations with anyone from any background and don't believe they're limited to middle classes, hence the reason I'm on MN.