Hi get1,
I can't speak on behalf of the trainer but perhaps I can leave you some food for thought. The fact is, parents do not have to be as good at parenting as adopters or foster carers. Or, to put it another way, adopters and foster carers have to demonstrate that they surpass the average parent in terms of their abilities to care for children and that they have to be more than just 'good', whereas parents just have to be 'good enough'.
As for the example you give of a chaotic drug user and their drug dealing husband 'keeping' their kiddy, it is only right that they should be given every opportunity to demonstrate that they can meet their child's needs and keep them safe. Sometimes this can be done while the child is still residing with them although sometimes it is necessary to find alternative caregivers while the parents are properly assessed and given the opportunity to change their lifestyle. The decision to remove a child is - and should be - a difficult one and situations that on the face of it appear to be clear cut rarely are and each case needs to be assessed on its own merits, so to speak.
Now, my experience of working with other agencies is, on the whole, a positive one and so I don't want what I say next to appear too critical. It's certainly been my experience as a local authority social worker that where it has been identified that there are concerns for a child's welfare, the thresholds of other agencies (like the ones you mention above) in terms of removing children are often lower than that of social services and that we would have many more children separated from their families sooner and permanently if it weren't for social services arguing - often in the face of quite hostile professional criticism - that responses to concerns need to be planned, proportionate, and, most importantly, mindful of the law and statutory guidance. Certainly, on the face of it, it would be easier to just be risk-averse and remove a child 'just in case' but that wouldn't be in line with evidence-based social work or the law. In fact, it would just be plain wrong.
I hope this goes some way to answering your question.