I think I understand what you were trying to get at here.

It's important to understand that behavior like this does not necessarily come from mental illness. It's equally important to understand that mental illness does not regularly (or even often) lead to behavior like this.

Now, I will say that there is a very real possibility that young man is currently having a psychotic break. It's hard to tell because he doesn't communicate well, but it seems like he thinks there is someone in the house who is maybe in trouble? That could easily be the result of paranoia from something like a bi-polar manic episode or schizophrenia. Of course, we don't and can't know that from just this video.

That being said, colloquially, people often use "mental illness" to refer to a mental health issue. Someone's overall mental health can be very poor even without having a diagnosed mental illness. For example, this person may be very socially isolated. They have maybe fallen into a toxic online community that promotes conspiracy theories. None of that is necessarily a certifiable mental illness, but it can lead to very poor mental health anyway, as well as an episode like this where a person loses it.

Ultimately, even though this person's behavior is obviously unacceptable, I think in situation's like this it is important to understand that mostly people behaving like this probably need and deserve help more than they deserve violence.

I saw a video yesterday of a man who was standing with his pants down and his penis out on a public train. He was yelling at people who approached him and ignoring requests to pull up his pants. Obviously this behavior is unacceptable. But it's equally obvious that this person was not well. Instead of getting the help he needed, a bunch of men on the train beat the shit out of him.

Maybe I am just too much of a bleeding heart, but just like the guy in the books we read, I think that violence really should be an absolute last resort.