If only D.C. residents had "Star Trek" phasers permanently set to stun. The Supreme Court would find the constitutional challenge to the District’s current gun bans so much easier to resolve.
Think about how different the problem would look: People could protect themselves without killing anyone. The weapons couldn't be used for suicide, and children wouldn't get hurt. The city's concerns about the dangers of lethal firearms would be satisfied, while citizens would still have effective tools for self-defense.
Science fiction fantasy? Yes, for now. But someday we'll have a perfect stun gun. And that technological improvement will significantly change the legal discussion of what "arms" the Second Amendment protects.
Of course there would be the inevitable howl of "Why do you need a stun gun in the mall?!" And not to forget the "Only ones".