Yet another religious cult raided

[Bun-Bun]

I'm not against the government acting in response to evidence of a crime, or even with reasonable suspicion investigating an individual. In this case, they did investigate and found out that the person who was fingered was the wrong person, and were unable to find the woman who reported the alleged abuse. Now 416 children have been forcibly removed from their parents by authorities, who are probably grilling them about their lifestyle. I mean, imagine that this was a Catholic Archdiocese in Boston where there were allegations that the Priest was fondling the little boys and the government swooped in an rounded up all the children of the parents belonging to that church. It's outrageous behavior, and excessive for the state to treat all the parents as abusers, or that the people are too afraid, "brain washed", or subjugated to resist or escape.

Predicate act: A report of abuse from the compound.
Official response: Investigate the complaint by going to the compound. The investigation is conducted with an abundance of manpower with an eye to the history of such groups and the capacity of this group to hide people and evidence.
Observed on the property: Pregnant minor females and minor females with children.
Extended response: Since a clear pattern of illegal and abusive behavior exists, remove the children. Investigate the compound for documents involving the age and marital state of the victims.

I fail to see what's so outrageous here.

Your analogy is deeply flawed, in any case. Your example presents a case where the abuse victim(s) are not under the physical control of the abusers. One would expect the authorities to take the actions necessary to investigate; in your example, I would expect them to question the children of the church members, possibly in a neutral place if there was any evidence of collusion with parents. Preventing further harm to the children merely requires the children not have further contact with the priest.

In the FLDS case, prevention of further harm would mandate removal of the children. It would also facilitate the investigation, but that could also be achieved by a neutral-ground questioning in the unlikely event the parents would cooperate. The key factor is the safety of the children.