Rather than deterring criminals, who will manage to have a gun in violation of the law, handgun bans will result in the unjust prosecution citizens who are defending themselves against criminals. Such an outcome is plainly contrary to the (misguided) intent of such bans, which is to protect law abiding citizens from criminals. A couple of example from the state of Illinois help illustrate the point: http://www.learnaboutguns.com/2008/07/09/the-injustice-of-handgun-bans-citizens-prosecuted-for-defending-themselves/
Handgun Bans
Cities that have handgun bans, plea bargin felony weapons possesion charges away when criminals are arrested. If they were serious about guns they would punish the criminals that have ILLEGAL weapons. If you are caught with drugs and weapons you should get a minimum sentence for each 10 years for drugs and another 10 years for possesion of an illegal weapon. But in the end they get 3 months for the drug charge.
On the other hand when a law abiding citizen with a LEGAL hand gun defends themselves the DA in most cities will go the extra mile to crucify these people.