Ban assault weapons!

Why on flat Earth could someone with the background of the Orlando mass murderer be cleared for purchase of, not only assault weapons, but any weapon at all more powerful than a sling shot?
Actually, why should any civilian be able to acquire any kind of assault weapons, – weapons whose sole purpose is to kill as many people as possible, in a short amount of time, and at a distance? Assault weapons are only meant for war, not civilian use! Short of making purchase and ownership of weapons in general more restrictive, a good start would be to totally ban assault weapons for civilians. Less powerful weapons are, of course, dangerous enough in the hands of the wrong people, but they are at least somewhat slower, while the need to exchange smaller capacity magazines, leaves a better chance for potential victims and others to interrupt the slaughter. Civilians running around with assault weapons, are unbecoming a civilized society! We better grow up from such madness!