I keep hearing the argument that ARs are designed for killing people, or that they were designed for military use. I'm really curious where that information comes from. Politifact shows that the later statement is false. Also, what is it about assault weapons that makes murder their primary purpose? Here's a semi-auto .223 Ruger Mini-14 that one might select as a hunting rifle:

You can purchase a 30-round magazine for the Mini-14. In which case, how is it any different from the SR556?

They both use the same bullet. Both can use the same capacity clip. They have the same rate of fire. Both can be obtained in a full auto version be law enforcement officials. You can mount whatever sights or scopes you like to either one. Functionally, they're identical weapons. Why is one of them now demonized? Is it because of the scary-looking black plastic on one? Seriously, I'm becoming convinced that the definition for assault rifle that politicians are using now is "gun that looks extra scary."
But would a ban on assault weapons be helpful? How many deaths per year are actually attributable to assault weapons? You can look at the FBI statistics on homicides, or the PolitiFact summary. In either case, it's clear that far fewer people are killed by rifles (either assault rifles or otherwise) than were beaten to death or were killed by knives. In fact, roughly the same number of people were killed by all "long guns (rifles, assault weapons, shotguns, etc...) as were beaten to death (by hands or feet) in 2011, and more than twice as many were killed by knives or other cutting instrument.
I will readily grant that homicides by handgun dwarf the other categories. Some 60% of homicides used handguns. My question is, why is the focus on assault weapons when they are not the real problem?
How often are guns used in self-defense? A number of surveys indicate that there are roughly 2 million defensive gun uses per year by law abiding citizens. Should we create 2 million more victims for the sake of the 8500 firearm-related homicides?
There's an excellent article on the whole issue here written by someone who is very knowledgeable in the area of firearm control.
EDIT: Neoteny kindly pointed out that I am incorrectly using the term "Assault Rifle" which is a highly regulated weapon. I should use the term "Assault Weapon," which includes the AR15 and other semi-automatic rifles. I was not previously aware of this distinction and will try to use the correct terminology going forward. The main points in my post should still be valid with "AR" and "Assault Rifle" replaced by "assault weapon." (I made this change above.) Apologies for the confusion.