I'm curious why you think anyone in DC should be going around strapped, besides law enforcement officers.
Because certain parts of the city are nuts and if you have to travel there, you should have the right to defend yourself.
Defend yourself from what? There's some conceivable situation where a gun could be useful. Those are way, way overestimated. You can be safe other ways. For example, always carry a decent amount of cash. And, it's also not that simple. Are you going to kill someone so they don't steal $50 from you? It's funny, people here are so anti-Death penalty but they're fine with some Chuck Bronson wannabe acting as judge, jury and executioner.
And, ultimately, the self-defense rationale for guns holds no water in a collective sense. Even if a gun makes you safer, the presence of guns makes the community less safe. You should tolerate some level of risk if it means that everyone can be safer.
What's to stop a fella from driving in from out of town if guns are illegal in the city? It's not a problem now, I don't see it becoming a problem just because of this law.
Why make it easier? If it's legal, people will have more access to guns in more places. Just statistically, more guns means more chance that a psychotic person will have a gun and decide to kill a Senator or Supreme Court Justice.