I'm reading two basic "arguments" - perhaps "positions" would be a better word.
1 - anything but the most effective and efficient is not effective or efficient at all. A knife may not be as effective as a firearm, but you would probably be surprised to find out is is much more efficient. Folks are less afraid of getting shot than they are afraid of getting cut. And unless you can keep every mugger/robber/rapist/Member of Congress* more than 21 feet away at all times, you are probably not going to be able to get to your firearm in time to "equalize" the contest. Action beats reaction, and all that. So having the most effective and most efficient still will not save your pretty pink hide.
2 - if someone is so dangerous that they cannot be trusted/allowed to have a firearm they should remain locked up. If they are "rehabilitated" their RKBA should be restored. I'm going to start on the MH side of the fence by discussing the schizo-affective. If you can convince them/force them to take meds they usually stop being delusional. But have you ever wondered why they do not want to keep taking those meds (besides the really horrid side effects)? Putting it in very basic terms, and skipping all the technical stuff - their delusion beats the heck out of their reality. So you are going to have to figure out a way to ensure that they are continuing to take their meds -- while dealing with the legal fact that they have a right to stop taking them whenever they want to. And the best way to determine they are still taking their meds is to do blood tersts, not wait till the residual stiuff has worn off and they go full-bore crazy again. Who's going to do those tests and who's going to pay for them to be done?
Now, for the plain criminal types, how are you going to "rehabilitate" them? (Actually, "habilitate" is the more appropriate term.) Anybody besides me read/reread Samenow & Yokelson's The Criminal Personality on anything approaching a regular basis? Folks, if you did not know, the truth is they think differently than we do, which pretty much explains why they act differently. There are ways to alter - not completely rewire - their thinking processes. In the 25+ years I dealt professionally with the inmate population I don't think I met more than 50 people who knew how to "treat" criminals to bring about habilitation, and I don't think I met more than a few hundred who understood the basic premises. Folks who came the closest were usually in the drug/alcohol treatment field and a lot of them were flying by the seat of their pants using personal experience of how they "got clean".
The criminal population is very much like the MH population - they are not acting out their dangerousness to self or others on a constant basis. But unless you can guarantee the ability to prevent an outbreak of dangerous behavior you are stuck with a risk. Our society is risk-aversive.
stay safe.
* - Member of Congress was not included to insult the other categories, but merely to round out the list.
