What did CPS think it was doing?
The first is that the CPS knew its actions were unjustified but was relying on the prejudice of the population and the court system to get away with them. On this reading the real objective was to drive the FLDS out of Texas and/or to destroy it. That is consistent with at least some of the evidence. It seems clear that, about three years ago, a local legislator introduced a package of bills to the legislature, some of which passed, intended to target the FLDS. They included an increase in the legal age of marriage with parental consent from fourteen to sixteen and raising polygamy to a felony. It is even possible, on this reading, that the CPS expected to eventually lose in the courts but believed, perhaps correctly, that they could impose large enough costs on the FLDS families in the process to persuade them to go somewhere else.
It is worth noting that the only justification offered by the CPS for seizing male children was that they were being brought up to be child abusers—which is to say, being brought up in their parents' religion. It sounds from some news stories as though the implicit deal being offered to parents was that if they would accept suitable psychological counseling, they would eventually get their children back. Combine those two and it looks as though the idea was to force people to renounce their religion, holding their children hostage until they did.
The alternative interpretation is that the CPS believed its own story. Based on the picture of the FLDS painted by anti-polygamy activists, primarily ex-members, they may have expected to find lots of pregnant minors, some of them thirteen or fourteen, and lots more minors with children. Having found them, they would then have sufficient legal justification for a good deal of what they wanted to do and sufficient public support for all of it. And if the story they believed was true, they were in fact doing their job, protecting minors from abuse, even if they were stretching the law a little to do it.
When they actually got control over the children, they discovered that the data were strikingly inconsistent with the theory. Apparently none of the minors were pregnant and only five had had children--a rate not far from the average teen pregnancy rate for the state. The CPS officials were reluctant to either recognize that they had made a mistake or admit it, so tried in various ways to fudge up evidence to support their actions. So far as public opinion was concerned, they mostly succeeded, with the help of major media too biased to do a competent job of looking at and reporting the facts.
In their defense, they were not the only people to believe the story. I believed it too. While I might have suspected some exaggeration, I assumed that the account given by defectors from the sect was substantially accurate. If I had been asked to predict the number of pregnant minors on the ranch, my guess would have been substantially above zero.
The evidence now available suggests that the story was not true, or at least not true of this community of the FLDS. Either things have changed over time, or the Texas FLDS community was different from the Colorado City community, or the FLDS defectors were giving a false and biased report from the beginning.
All of those alternatives are possible. What is not possible is that, in a community functioning as the FLDS was said to be functioning, where girls just past puberty were routinely married to much older men and forced to have sex with them and bear their children, no minor was pregnant and fewer than a fifth of the minor women aged 14-17 had ever had children. Yet those, apparently, are the facts of the Texas case.