In most cases, though, you can get those individuals on actual charges. People aren’t usually violent completely out of the blue and a suspicion of future violence might come from prior acts of violence or securing materials for mass violence (like building explosive devices)…
The rationale for detaining someone for public safety is almost always coming from prior acts that we have laws for. We should force law enforcement to actually use those laws since they’ll have a burden of proof to enact enforcement… the IPP loophole is awful because it leaves no legal recourse - there was no trial you can appeal or at least argue against.