Children are only removed as a last resort. Mistakes are made with children removed unnecessarily but they are rare, rarer than the number of children left with parents too long.
My friend is the head of childrens social work for my county, she has 2 women who have had 17 children removed between them, both drug addicted, alcoholics, and earn money from the oldest profession. Alas, they have tried everything to persuade both women (who know each other) to stop getting pregnant, residential rehab, then access to the non adopted children, even a promise of a new council flat each on condition of long term contraception - all failed, one is pregnant currently.
So sad all around, it's a vicious cycle for the women and their damaged children didn't ask to be born.