The proper way to deal with leftists is to troll them. They hate reason, facts, and arguments. They will either put you on trial for heresy or dismiss you. The appropriate response, then, is to make them angry while maintaining your superiority. Here are Fearsome Pirate's Rules of Trolling:This is quite a good list, and is particularly good food for thought about how to engage in gun control discussions. In fact, it reinforces my preferred approach of saying that I'm not opposed to gun control laws, just to stupid and useless ones. A more in-your-face approach would be to ask why your opponent wants to oppress women, gays, and minorities (all of whom are hurt by gun control laws).
1. Keep it short, stupid.
RTWT. And I will have to go back over there, as he has a tag for Aquinas.