Quite she means that people seem to think that social services can magic children out of family situations which are imperfect but not awful and make everything better either with "support" for the parents (who of course would immediately be gushing with grace and happiness that social services offered this, and not defensive at all) or perhaps by removing children from the home that they know and are reasonably happy and settled and at-least-mediocrely looked after in and placing them with a nice infertile couple somewhere who will love and care for them and be perfect parents.
Or perhaps what's really meant is that they want/think social services will scare the parents into better behaviour and/or punish them for not conforming to some MN parenting standards people have made up in their heads, and that this will cause the parents to see the error of their ways and change and everything will be well again.
In reality - no. A social services investigation is terrifying, even if you don't think you've done anything wrong. It's basically a reminder that people exist who have the power to take your children away for good which is a very primal kind of fear. Scared people do not act in their own best interests as they tend to revert to instinct as the overload of adrenaline prevents rational thinking. Like the way that somebody might shout too loudly or even smack or shake a child who has just acted in a way which endangered their own or their siblings' life.
Social services are stretched and do not have endless resources to offer support. So even if somebody does not act defensively and angrily and is receptive to offers of help, the help offered is likely to fall far short of what is actually needed. It will not usually be extended long enough to be valuable and so it often does not actually solve the problem. There are certain situations where contacting SS for support might be helpful but I believe these are few and far between. Usually support is targeted towards families who are actually in danger of having children removed, since it can actually do more good here.
Additionally, most people don't see any problem with the way that they currently behave, otherwise they would change the way they behave. It takes introspective thought to change one's own beliefs and thought patterns and social services or their supportive resources do not have magical mind altering beams (which I'm sure we're glad of!) so it has to be a person's own decision to change. In most situations where social services is suggested on MN, this is not the most effective or efficient way to change someone's view, in fact because social services tend to be seen as a threat it's an especially ineffective way to change someone's views and the poster would be better off trying to support their friend themselves or point them towards services which might be able to help them in a more understanding way.
Lastly, yes social services can remove children, but this isn't like rehoming a dog because the owner doesn't have time to walk it properly and it is getting overweight. Children unlike dogs are human and humans form extremely complex bonds and attachments. The attachments children form in their early years are essential to their future development and breaking any attachment, even if it is not a healthy one, is harmful and causes damage to the child. Children who are removed from parents are almost never moved immediately to a permanent adoptive home as the best course of action would be that the parents make the necessary changes and the children can return. Which means that children in the care system are moved to foster homes, where they will have to adjust to being cared for by a complete stranger, will come into contact with other children who have been exposed to likely far worse things than they have themselves who could have extremely destructive or harmful behaviours. They are not able to be told by anybody what is happening to them long term which is hugely unsettling and of course most importantly of all they have absolutely no choice or say which must be terrifying, and which all together makes for a traumatic experience - again, trauma harms.
As the care procedures can be long and complicated children are often moved in and out of foster care, often between different foster homes which compounds the trauma and sense of loss especially if they form new attachments to have them broken again. Even if a child is both unlucky enough to be unable to return home and lucky enough to be approved for adoption very quickly, it's still a traumatic experience to be taken from everything you know and placed with strangers who you are expected to learn to love and attach to. It doesn't matter in this case how nice the new adoptive home or parents are (and I'm sure, adoptive parents aren't perfect, like any parents) or how poor the treatment or environment at the child's home was, the child is still out of control, still experiencing a loss and the experience is likely to be traumatic. As mentioned, most children involved in the care system are not this lucky.
In short, it harms children immensely to be removed from their birth families and placed with a new one, no matter how lovely the new family is. That is why this step is only taken in very extreme cases where the harm from staying in the birth family is likely to outweigh the harm caused by removal.