Simple philosophy principle, if A is true, if B is true, and A + B = C, C is true
A) if someone does not possess a gun they cannot shoot someone
B) guns only kill lots of people if someone shoots them
C) people who posses guns and shoot people can kill people. People who do not posses guns cannot shoot guns and kill people.
We understand that A and B are true. C is a combination of A and B, therefore C is true. If people don't posses guns they cannot kill people. Obviously taking away guns from the country that has the most guns in the world would be a very challenging undertaking; though maybe one worth trying. We could also try to 1) stop selling guns, 2) stop selling ammunition and ingredients to make ammunition, or 3) require all registered guns be inventoried immediately with a governing body and regulate how many can be owned, possessed...etc.
Think to when people made bombs out of fertilizer, making bombs was illegal, but buying tons of fertilizer was not. What did America do? They didn't take bombs away from people, they heavily regulated the sale of fertilizers and other combustible organic products. Maybe it's time to do the same with guns and associated paraphernalia