A 12th-century common-law right becomes a cudgel to prevent common-sense regulations that could constrict the easy availability of weapons.
In a nutshell:
If we disarmed you, criminals who are forbidden by law to have weapons would become harmless. We should be more like England. I come out at the end and admit this wouldn't have had an effect on the latest shooting I'm prattling on about, but I'm smart and sophisticated and obviously not primitive like you, and this is how I define "common sense."
Fanatical certitude based on ignorance--talk about your 12th Century mentality. It's hard to recall the last time I read so much concentrated stupid in one place--at least by a grownup.
Oldsmoblogger has a more detailed take on this.