Just having a look at causes of death and crime rates in Australia. The latest figures I can find are from 2009.
Here are the ones for weapon use.
In 2009, a weapon was used in 77% of attempted murders, 66% of murders and 43% of robberies (Table 2.6).
A knife was the most common type of weapon used in committing these offences: 37% of attempted murder victims; 36% of murder victims; and 19% of robbery victims were subjected to an offence involving a knife.
A firearm was involved in 18% of attempted murders, 12% of murders and 7% of robbery offences.
A high proportion of sexual assault offences (98%), kidnapping/abduction offences (83%) and over half of robbery offences (57%) committed did not involve the use of a weapon.
So even if we did get rid of all weapons - including knives and guns - crime rates won't change much.
So if it's not the weapon, it's ???