While you are not wrong that there are other ways to commit mass killings, in pretty much all countries with no guns, you don't see these alternate events.

So the outcomes you suggest are perhaps not the logical outcome of removing guns from society.

As an example if I take Europe as a whole (the bits not in an active conflict) there aren't 600 events a year of water poisoning or trucks in crowds etc.

Now true, they have different approaches to handling mental illness, so that's a factor, but even so.

Trucks have truck licenses and are expensive to obtain, or require getting a job and passing screening.

Lighting up buildings, destroying a dam (how??) and other civil engineering misadventures require way more thought and planning than shooting someone with a gun in your cupboard.

Limiting gun purchases is way easier than tackling all of mental illness. We can't even define half of the reasons why people turn to the 'dark side', let alone be there for them in exactly the right capacity at exactly the right time to save their mind.

For sure the psychiatric care in the US is far from sufficient, but that doesn't remove from the fact that guns make causing massive suffering accessible in a way that building a bomb and blowing up a dam doesn't. Guns shouldn't be allowed to be sold OTC, and mental health issues should be taken seriously. Both problems have to be adressed.

Mental illness surely is a factor, but I don't think it's what pushes people over the edge.

Remembering my teenage years, the times I acted badly were because of anger. Extreme frustration towards a society or people who I felt treated me unfairly.

The hardest to deal with was (perceived) hypocrisy from people who were in a position of power.

Looking at US media, politics and justice is infuriating as an outsider. Everything that's done under guise of "freedom" and "democracy". All the "morality" work from people who by their own standard would go straight to hell. Zero accountability for anything.

Trickling down might not work for money, it surely does for the poison that this system produces. At least in openly totalitarian countries, people get a chance to see their government for what it is.