The standard response to liberalizing CCW or allowing self defense is that it'll lead to "Dodge City" (which actually was rather peaceful compared to modern inner cities).
It's already here, as this Washington Post article illustrates.
Facts: a guy commits two murders, on the street, in front of dozens of witnesses. Despite offers of relocation and witness protection, only one will testify. The second murder, BTW, was of a witness to the first murder whom the perp thought (incorrectly) might be aiding police. Guy wins two acquittals.
The mother of the second victim starts investigating, and is warned her house would be shot up if she didn't stop. She stops and moves away.
At least in Dodge City you could shoot back. And in Tombstone, you could bring in John Slaughter, tell him to do what he had to, and you'll look the other way so long as he hurts only the bad guys.