Just throwing this out there, In my opinion, there should be some sort of education of the law before someone is allowed to own a firearm. I know here, north of the border you must take a safety course to own long guns, and then a separate one for restricted weapons (handguns) and both of the courses integrate safety as well as education on the laws surrounding gun ownership and usage.
my 2 cents
In the US, ignorance of the law is not an accepted defense. And you can buy a number of dangerous things without required knowledge of all laws which pertain to it.
EG. can you get a driver's license if you miss some questions on the test?
Do you know that mixing bleach and ammonia and releasing it in a crowd is illegal?
Do you know all the Arson laws before you are allowed to purchase gasoline?
But, "allowed to own a firearm" means the individual has no right to own one, and possibly no right to self defense. If you are comfortable with that then stay where you are.
What you are suggesting is restricting gun ownership so it is a privilege and not a right. Some governments do not trust their populace with guns. Some governments believe people are guilty until proven innocent. (Some forums do, too, without knowing all the facts in matter.)

Some like to speculate the real law based on their own opinions. I just hope you find a judge/legal system that agrees with such opinions.
In principle, the U.S. persons are free to choose between evil deeds and good deeds. The laws are usually created to punish the evil doers after the fact, and act as a deterrent under threat of punishment. There is always a choice for the individual, which many governments wish to remove from the individual.
I posture that if one actually succeeds in removing all evil deeds, good deeds will also be prevented.
In actuality, governments will be the sole provider of evil deeds, if successfully removing evil deeds from the general populace. As, the general populace won't have any say in the matter because they are all evil if not a part of or in approval of their controlling government.