Restricting weapons causes injury.
Not necessarily. Your logic is terribly flawed.
1. Just because weapons are not restricted does not mean that all people will choose to have said weapons. Those who choose to not have a weapon are vulnerable to those who do have a weapon.
2. If, contrary to point 1 above, everyone chooses to have a weapon, then the number of injuries due to accidents, twitchy fingers and rage would likely rise.