On the other hand, for the longest time both DC and Chicago virtually banned guns and yet had atrocious violent crime rates.

There’s an abundance of evidence (e.g. [1]) that nearby states with more lax controls produce a flow of black market guns toward states with tighter controls, and that with increased legal availability the price of a black market gun declines[2].

1: https://www.nytimes.com/interactive/2015/11/12/us/gun-traffi...

2: http://www.ibtimes.com.au/cost-illegal-firearms-australia-ha...

I like that it’s a very convenient argument that rationally culminates with “so the only way it can work is for everyone to ban guns everywhere.”

Not necessarily. It only leads there if the flow has to be zero - reducing the flow and/or making black market guns more expensive than alternatives would still be worth doing (it would have a significant effect on armed crime long before the number of available black market guns reached zero), and could be achieved through some degree of owner responsibility (e.g. requiring guns be in a safe, have trigger locks, be kept separately from ammunition, limit the volume of ammunition stored at home). Better still, that doesn’t even have to require legislation!

Some of those steps would also most likely reduce the number of unpremeditated killings, e.g the freak accidents where babies shoot parents with the gun in their mother’s bag, kids shoot each other with a gun taken from a nightstand etc.

Of course, the usual response to this is some variation on a theme of the fear of crime, to which the only response is that violent crime has been declining for years and the people making most noise about it are frequently invested in the weapons industry.

I don't have a problem with Chicago enacting gun free zones and stopping all people and vehicles entering the city for cavity searches to stop the flow of weapons. I think it would be an illuminating experiment.

I suspect people might still find a way to smuggle things through the roadblocks but they could always build a wall.

And then there is the possibility that murder rate has no connection to gun control..

Did UK murder and violent crime decline after gun control? And if so, was gun control the cause?

https://mises.org/blog/gun-control-fails-what-happened-engla...

That’s an intersting source that appears to have an agenda. The opposite side of the equation is probably something like this https://www.google.co.nz/amp/s/amp.theguardian.com/us-news/2...