People were just as dangerous to other people before explosively propelled heavy metals.
However, people like to look at an icon; I don't know the reason why they do that. Perhaps it's to protect oneself from the fact that there's people out there who will harm you for personal gain. They often use an object to give themselves an advantage. If there were no firearms, it could be a club; one whack with a club will do the same job as any firearm. These types take you unawares most times, so it doesn't matter if the range of said object is short--spring propelled projectile weapons exist, and they've been used countless times in history (bows).
There's an argument that modern, high capacity weapons equate to large scale murder; that's true, but large scale murder can be inflicted by many means (examples for both are there), and it has been.
Better awareness by teachers and carers on the signs of a potentially violent individual, from as early an age as possible and therapy for that from the same early age, will help more than any restrictions on an object. You can never stop it completely though.
I've noted that the anti-bullying implementations taking place now at schools here, which was never there when I was younger, has helped a lot to create a more peaceful environment to grow up in.
As an aside, my firearms, bows, swords and fists will never harm anyone (there's always self-defense, but I have no bravado and I loathe to hurt another, as they often have no say in it, just like I have no say with my ASD).