It’s just incredible the injustice that can be done in the name of protecting children. I really do wonder if it’s cultural or some kind of innate psychological irrarionality that seems stronger in some than others. I love kids and care deeply about their welfare, but people sometimes try to make me feel bad or that I’m the weird one for being able to think (I believe) fairly rationally about the risks and dangers that they face, instead of massively over-exaggerating!
Or of course the opposite, keeping an appropriate eye on relations and acquaintances when people assume they’re totally safe but it’s actually somebody with that level of relation who’s likely to be a danger than a stranger.
This is just speculation, but I bet those groups (or their members) aren't always calmly and coolly trying to find the best policies protect the welfare of children. Instead they feel themselves on a kind of righteous moral crusade, and what's more heroic than swooping in to take the child away from the clutches of the villain? The feelings of heroism could obscure understanding the harm the "heroic act" could cause.
Mostly they are operating on priors. The prior probability of a separation being the right thing to do is very high, because they have a _long list of mitigation before they actually can take a kid away. In the case of a doctor-approved immediate physical danger, they are regulated into acting on behalf of the immediate safety of the child while the investigation is ongoing but even that is considered temporary.
The goal of any foster care situation is to get the kids back with the biological parents, so time is on their side, provided they are not living in a circumstance that disallows the kind of attendance and involvement that the state would require to clear a caseworker to re-unite the family. Sadly, many are.
Source: Foster parent.