This is inaccurate. Guns are designed for many purposes. That is like saying cars are designed to cause accidents.

The light gas guns that NASA designed and uses to simulate micrometeoroids so they can develop better protections for spacecraft certainly were not designed to cause harm to humans and it is actually harm if the target is a composite honeycomb.

I own guns that were absolutely designed to be used for target shooting (not to harm someone or some thing) and would be a poor choice if you intended to harm someone.

You are oversimplifying or are just ignorant in regard to firearms.

Are acids designed to cause harm? Is harm always bad?

TEK