You banned cocaine, I can still buy cocaine. You made a trade embargo on cuba, I can still get cuban cigars. You banned illegal immigration. I still have illegals mowing lawns down the street. You banned murder, I can still kill people. You banned robbery, I can still rob people. You banned assault rifles, I can still get assault rifles. You banned hacking, people still hack. You banned ______ youtube video in my country due to copyright laws? Let me just download it off the pirate bay.
The only thing gun bans do is bar the law abiding people from getting guns. If I wanted to murder an entire movie theater full of people, a gun ban would be the least of my concerns.