The first "false" premise is that if you could find a city with NO guns, and intruduce some, gun death would go up. No mention of places like Chicago where no one is supposed to carry. .
By itself, this is true. Without guns, no gun violence. Duh.
However, OTHER violence from simple assaults to battery and knife violence would escalate. Muggings, thefts and burglaries would escalate. Racketeering would increase. Generally, property rights would be endangered, and the weak members of society would be at the mercy of the predators.