Indeed this is a difficult matter and we're sailing on murky waters here...
The trouble with fighting for human freedom is that one spends most of one's time defending scoundrels. For it is against scoundrels that oppressive laws are first aimed, and oppression must be stopped at the beginning if it is to be stopped at all.
Even though I don't agree with many of the other things this particular gentleman wrote, this quote hits the nail on head. Unfortunately. Good and evil do not always translate directly to right and wrong...
If legislation offers loopholes for deviant sects to exploit, it's not really acceptable for a government to work against their own laws. If that's the case, change the legislation so there's no more loopholes. It might be difficult, though.
Personally, I don't see what the problem is in not getting this Super Adventure Club out of commission. What is it exactly that makes it non-punisheable for these people to marry and have sex with 13-year-olds, or underage girls in general, and abandon the required 2/3rd of boys so that every man can have at least the required three wives? It can't be a matter of not being able to prove it. So is it unwillingness to gather the evidence then?
Another fundamental question arises: Should the decisions of a brainwashed, legally adult cult member be respected or should they be, so to speak, "saven from themselves"? It's pretty probable that many in the cult really see nothing wrong in the daily life, but if they are of age, it's not really anyone else's business as long as there's no crimes committed, no matter how twisted the ideology may seem to normal people. So it seems the actual question is, should children be allowed to be brainwashed?
That in turn is even more tricky question, because it translates to who has the right to be a parent, and what kind of belief systems are correct for a child to grow in.
It would seem that to solve this problem, a law would be needed that disallows people who have strong ideological commitment to ideas that contain illegal elements, from raising children.
It's of course obvious that this kind of legislation would never really work out and it would either simply not be enforced, or it would be really easily misused and it would turn the country into child concentration camps where the Right Ideology, Ethics and Morals would be taught to children, away from their deviant, communist, terrorist, fundamentalist parents.
Being obvious that this kind of approach doesn't really work no matter how much people in mainstream society would just want to help, what other choices are there? One thing that comes to mind is making it more difficult fot cult organizations to survive. Divida et conquera, as they say. Revoking the tax exempt status from all religions that don't really contribute to general community would be a brilliant step to right direction in my opinion. It would make it that much more difficult for all cult leaders to operate - of course, for cults such as FLDS it would have much less of an impact than it would have on, say, Church of $cientology, but it would affect them too, I'm quite sure.
Aside from that... I've got pretty much nothing. Oh, I know. Enforcing children to go to actual schools and tightening the parametres of acceptable homeschooling (ie. you need some pretty good criteria for being allowed to be homeschooled). If you make the children have normal contact with normal people and learn normal social and academic skills, they not only might have an option to leave the cult without ending up as hobos and castaways in mainstream society, but they also might have the incentive to do so.
These might be a good way to, so to speak, enturbulate the cult leaders in their comfy little lifes filled with schemes.