If a mother is having rhe "shit beaten out of her", kids are not removed as the first option, social services try to work for the safety of the kids and the mother, and part of that, yes is not allowing rhe partner back into thr family home and round the kids. If the mother continues to allow back repeatedly the violent partner, and the violence continues then yes social services will act to protect the children.
That's not about class, or what you drink, or how much you smoke. It's about the fact children cannot be brought up in an environment where violence is prevalent in their home.
Social services don't take kids because you smoke, or because you prefer one tipple over another, or because you're a single parent, or because you're autistic.
They do take children for many other reasons, and yes one of them is continued domestic violence in the home. If a child is at risk, be it of harm, neglect, physical, emotional or both, then social services will act. But removing rhe child is the last option and only done if all other options have been exhausted and the break in the family bond is deemed much less damaging than leaving rhe child in that environment.