So, theoretically, if it was just as easy to kill lots of people with a pressure cooker bomb as it is with guns, then you'd see just as many pressure cooker mass casualty events as you do mass casualty events with guns. But we don't. When someone wants to go out and kill a bunch of people, they almost always choose guns. That suggests that when people want to kill others they believe they have a better chance with guns than pressure cooker bombs.