My "we need to try something" is an acknowledgment that if we don't make some steps we are going to end up losing our guns. They continuously point at us and say that we have no suggestions and we fight any attempts to make progress and honestly it is a fairly convincing argument because we contribute very little towards any sort of prevention effort.
The right even fought against the CDC from conducting studies on firearm deaths which make us look like we don't even want to define the problem. Trump recently signed the legislation that rolled back part of that law and allows the CDC to study gun violence so maybe we are going to make more progress on defining the problem at least.
We keep certain sexual predators in jail past their jail sentence if a mental health professional deems them too likely to be a potential recidivist, so there is some legal precedent for jailing people on risk based factors. Now maybe you are against that policy with sexual predators too and that's fine. I can certainly see a slippery slope argument being made, but here is the thing: A threat isn't always clear but that doesn't mean its not a threat.
I think my suggestion to the problem you point out is that the red flags that people see should be the beginning of an investigation by appropriate authorities. If we see all the red flags in someone and sit back and just shrug our shoulders on the justification that the person hasn't committed a crime yet then we are missing the opportunity to prevent something. But if we notify law enforcement who makes further checks of the person's background and is able to investigate then maybe they will find evidence of a clear(er) threat that can be acted upon.
You still don't get it.
WHO decides what the red flags are? I'll tell you who ---- lawmakers, politicians, and anti-gun groups.
Member of a militia? RED FLAG!!
Member of an alt-Right or White Supremacist group as defined by the SPLC? RED FLAG!!
Member of the military serving in a combat role? RED FLAG!!
Bought more than 250 rounds of ammo in 3 months? RED FLAG!!
Member of the NRA? RED FLAG!!
Red flags don't have to be based on actual evidence that they predict behavior, just like trying to ban a specific type of firearm doesn't have to be based on evidence that doing so has any impact on crime -- the CDC reported there's no evidence to support an AW ban. it's just a shoehorn into taking guns based on criteria that can be CHANGED to disarm anyone the lawmakers decide are "scary". (e.g. "Deplorables").