I agree that for some children adoption doesn't work, but adoption as a whole does work. I'm not commenting on anyone's particular case as much as on adoption as a whole. Not looking to blame parents either.
Social services should not treat adoptive parents like criminals unless there's proof of mistreatment, they should be teaming up with them and do earlier interventions, that's something I agree with too. I think most social workers have the best interests of the children at heart, but as you mentioned things get complicated with the current state of the law.
I've known my fair share of adoptees growing up who come from complicated situations or dangerous birth families, I've seen the impact that trauma can have on them and I believe the same as the people I quoted before (from the BBC investigation) mentioned; in a lot of cases, things could have been different with earlier intervention. But cases where things will just go downhill exist, and it's a shame because it's something that sometimes can't be predicted.
What I notice with families in crisis (not only adoptive families, but all of them) is that the parents are immediately blamed, when it's more complicated than that. Parenting isn't everything, parents don't have the monopoly of influence on a child (especially not past the age of 12), children can struggle with pain and shame and with making sense of their place in the world: for adoptees you already know the load that is added, cases of earlier mistreatment and complex trauma, sometimes idolization of the birth mother (who can be decent but troubled or can be, frankly, a bad person), sometimes demonization of the birth family which can make them believe they will end up being just as bad. And the safest people to lash out at is their adoptive family and/or themselves.
But child on parent abuse and estrangement is on the rise in general too, and even if there's differences with what biological families go through, there's similarities too. That is what I meant when I said that in adoptions, the issue is often exaggerated; I don't think for a second that parents are lying about the severity of what happens, but that this issue is not unique to adoption, although it is more prevalent. It's not as if families related by blood are basking in eternal love and harmony (which is something that adoptees seem to think sometimes??). I've seen sons and daughters beat their parents up or steal 40k from their bank account. There was an article a while ago about sons murdering their mothers.
Sometimes all it takes, birth family or not, is a child mixing with the wrong crowd because they feel unloved and insecure despite being raised in a loving home. Maybe they are different in a way they can't reconcile with what they feel is expected of them, maybe they are angry at the world because they think that others have it easier, maybe they were abused by someone; either way they struggle, sometimes don't even know where those feelings are coming from, much less how to deal with them. It's a complicated situation all around, but I believe that support would help in most cases. In others, however, it will not. And I don't blame parents who decide that enough is enough after years of being terrified in their own homes. I simply think adoption works in most cases, even if in others it does not.