Parole boards.
We are not talking about dangerous "ideas" but people who have been convicted of the most disgusting and egregious crimes against children.
The guy in this test case was guilty of receiving child pornography online. The government decided to keep him indefinitely 6 days before his release.
Are you saying there is no chance of a slippery slope here? That it's OK to indefinitely detain someone who downloaded illegal child porn, but NOT someone guilty of violent assault? Weird. If it makes sense to keep this guy locked up to protect us, then why shouldn't they protect us from other dangerous criminals? NOT FAIR!!!
In the case of child molestors, you have 1) high recidivism rates and 2) linkage between behaviors. If someone is convicted of molesting a child, is in prison, and then views child porn before release, I have no problem with extending his sentence - indefinitely if need be.