Crazy people have all day and all night to think up ways to hurt others. Their focus is on inflicting pain and suffering and some have genius or near-genius mental powers to devote to the task. They will use whatever is available. If they can't get guns, they will use poison, knives, cars, shovels or anything else that might do the trick.
Crazy people always get the first swing. We have laws against assault and the police frown upon you restraining another person with handcuffs or ropes. It's not going to end well if you lock another person in the basement and feed them once in a while. Crazy people are allowed to roam freely and you can't take preemptive action, no matter how dangerous you think they are. If the crazy person has a history of attacks where their weapons show escalation of danger, you can't do anything to them until it gets lethal or practically lethal.
When an attack gets underway, you can't always call the cops. Sometimes you're busy defending yourself and trying not to be killed or maimed. Sometimes you're hampered by a desire to not kill the crazy person attacking you. When defending yourself, it helps to have some weapons at hand or training in martial arts. I was always lucky enough to be able to use the latter and prevent things from getting completely out of hand.
Calling the cops isn't always the best idea, either. By the time they show up, it can be either too late or the scene will lack any evidence of who started it. I have a couple of friends who ended up in jail because they were defending themselves and the cops believed the crazy person.
This is an excerpt from the US legal code. I don't know what it does, but it's the kind of thing people think is going to stop crazy geniuses intent on committing mayhem.
(a) Sections 452 through 459 and section 462 of this chapter shall also apply to the United States Court of Federal Claims, to each court created by Act of Congress in a territory which is invested with any jurisdiction of a district court of the United States, and to the judges thereof.Right.
(b) The official duty station of each judge referred to in subsection (a) which is not otherwise established by law shall be that place where the court holds regular sessions at or near which the judge performs a substantial portion of his judicial work, which is nearest the place where he maintains his actual abode in which he customarily lives.
Crazy people want to hurt, have time on their hands, are imaginative and get to attack first. Laws and cops are all well and good, but when things start going sideways, I want a weapon close at hand.
Personally, I want an AR-15 with the Harambayonet. ;-)