“The conclusion is, if some significant portion of the population cannot use something responsibly, we either have to ban it for everyone, or somehow license it to people who will not misuse it.”
That’s where I can’t agree with you, because I don’t see how your logic supports that conclusion. There are thousands of things out there that people can choose to use responsibly or irresponsibly, and we are not forced to make the conclusion you suggest. Instead, we just let the irresponsible people suffer the consequences for their actions when it affects only themselves, and punish them legally or civilly if their irresponsibility effects others.
If you really believe that, then lets discuss dynamite. Its usage currently requires an explosives license, but if I am to understand you correctly, you have no objections to letting anybody play with it. Do I understand you correctly?
How about pharmaceuticals? Apparently you feel that people ought to be able to prescribe themselves whatever medication that they see fit, rather than licensing doctors or Pharmacists. Your position seems to be: "We don't need no stinking license!"
If you can't follow my logic, I perceive that it is only because you don't want to. It's easy to follow, but some people do not like where it leads.