"If everyone has a gun, they can defend themselves!"
As Bloke says, the more available a weapon is, the more commonly people will use it for misdeeds. More crime, more deaths, more idiots who can't handle the power of a firearm.
"If no one has guns, there will be less crime and murder!"
On a small scale, petty thieves and idiots no longer having access to guns lead this to be true. At the same time, larger criminals now have a huge advantage over civilians who can't defend themselves, as well as any police forces not allowed to carry firearms. This "advantage" lets criminal organizations get away with more terrible deeds, and more often. Lesser crimes (not that manslaughter is a "lesser" crime...) more often, or more serious crimes more often (bank robberies, massacres, etc.). Whether or not either can be considered a lesser evil is irrelevant, since gun control or gun freedom can't come anywhere close to completely ending the problem.
And just for the sake of mention, gun control statistics show it really doesn't work. People hell bent on crime 'n murder will still take their blades 'n home-made bombs to the battleground. Since their targets won't have guns, it's even. Just as if criminals and civilians might cross each other and both have a firearm.