People breaking the law are -BREAKING THE LAW-. Please explain to me how banning assault rifles will stop someone from killing people. They're either going to buy the exact same gun illegally (which many of them currently do; IE the high-cap magazine in the aurora shooting) or find another way to kill people (which many of them currently do, IE the Boston marathon bombings). Banning weapons only affects the people who already follow the law, and they're not who you're worried about.

Why do you need an assault rifle? Why do you need anything more than a pistol for self defense and a hunting rifle for hunting.

what if the criminal has body armor (it's actually pretty common)
people hunt with ar-15s all the time

The second amendment was put in to make sure that the people as a whole remain stronger than the government, thus avoiding the possibility of a dictatorship. It has nothing to do with hunting.

When was the Bill of Rights written?

The founders never imagined tv which can sway people's political opinions to those who have the most money, nor the internet which can defame people rapidly. The first amendment still applies to those, right?

If you're gonna make an "assault rifles didn't exist in the 1800s" argument, it's rather irrelevant. The entire bill of rights goes after the same purpose of "the government should be limited in power and the people should be stronger."