Aretae, as is his wont, brings The Smart.
What I like about this is that by starting the discussion from the perspective of a hypothetical thought experiment, it breaks the participants out of the emotional starting point that drives 99.9% of them. At that point, there's the opportunity for the Buddha to lead them to Enlightenment.
The one thing that I'd add (because unlike Aretae, I can get pretty nasty) is when the Progressives drop back into emotion (because they don't like having to argue actual outcomes) it offers the opportunity to say "This is the problem with Gun Control. It's not rational, it's hysterical. No wonder it doesn't work." That will usually close down the conversation (and leave everyone thinking that Borepatch needs to learn some manners), but has the virtue of letting everyone know precisely where I stand on the issue.
It also has the virtue of being precisely correct, which just annoys everyone even more.