RL problem: Guantanamo. And that later Americans learnt that trying to imprison such people is so complicated from legal perspective that it is much less fuzz to just use drone. Later, the procedure was even improved further, so some inmates were released because of lack of evidence, immediately afterwards those "innocents" joined some terrorist organization just to be droned at first occasion. (I could point out a few more such cases from RL, but I think that with this the most people would be familiar with. It seems that in this case the applied solutions, even though more or less in accordance to law was neither specially practical or humanitarian)
(setting: near future, post-apo) The challenge is the following:
1) To have a rough idea for a law that would allow to imprison people who seem possess serious threat to society, while those people can not be proved yet of any specific crime. (just seem to be co-involved or planning something nasty)
2) The law should be actually really hard to be used against any peaceful opposition, even if they poses clear threat to wellbeing of the group in power.
3) There is not much public opinion left, so no problem about that. To the society such regulation is being advertised as reasonable solution in accordance with utilitarian ethics. Thus this regulation would have not to blatantly violate aim of society happiness maximization.
4) The idea is not to put a few very vague and harsh laws concerning conspiracy, being co-involved, failing to report crime, etc and use them selectively. But to drop whole idea of "guilty" and "punishment" and instead "threat" and "isolation". Actually, if that would not increase the cost too much, those arrested people may be treated nicely. (after all, it's nothing personal, and at least some of those people may indeed be innocent, so no reason to apply unnecessary cruelty)
5) The law is not written against any specific group, but more in general, there is no idea who next would be a threat, nor whether the threat would be from outside or inside.
6) The solution is based on law that actually allows that, and not unofficial gov policy to be reasonable in breaking its own law.
Any ideas how such regulation would look like?