Known Unknowns and Unknown Knowns

So. Bans on things. Like guns.
What works? What's up with that? What's the purpose? How can it be achieved? What other fallout is there?
Nobody really has any actual data. The Right has fantasies about guns in every hand preventing violence, the soft-Left/liberals have notions that banning certain kinds of guns would have some sort of effect on the murder rate.

Why does my man card need to be reissued? Did it expire? 

The NRA is basically the soft-hearted liberals fantasy of a gun's rights organization. I mean, they're nuts. But in my opinion the biggest damage they've done is to prevent any research at the Federal level on gun violence. Which is why nobody can get any real numbers. About anything.
And that may indeed change.
If it does we might discover some unfortunate things. Like that black assault-y-looking guns actually do attract people who want to shoot up a school. Or that stop-and-frisk saves lives. Or that neither do. Or that one or the other. Or something else.
But until we're allowed to have some non-nonsense analysis it's very hard to tell what will work.
In the meantime the NRA likes to pretend it does a great job for gun rights. Right now it's doing a great job at frightening moderates. And that's not good for gun rights.
For the longest time the NRA blamed "diversity" in American society for the outsized amount of violence in the US compared to other similar countries. In Bowling For Columbine Charlton Heston even starts to say that, and then he makes a face and corrects himself. Luckily for us even he realized what kind of dopiness that was.
The comparison between the US and Canada is very interesting. Just as Michael Moore began exploring that comparison he bailed out. It was a very interesting disconnect in the movie. Why does Canada have so many fewer murders per capita?