It's because you have too much freedom, you dim-witted, common citizen.
We need a nanny-state watch dog to lord over you so that bad things would never happen.
Arizona Aftermath: Permit-Free Carry Law Prevented Law Enforcement From Having an Opportunity to Stop Jared Loughner From Carrying a Gun, Says Mayors Against Illegal Guns
These asshats are telling you that freedom is the cause of evil.
Update - Kurt Hofmann has more thoughts on Mayors Against Freedom