I'm not getting the "designed to kill" argument.
Guns in America are legally owned for two purposes...hunting and defense.
Yes, military firearms become sporterized...been happening for more than 300 years.
I own the civilian version of the M-16, it was the first semi-automatic firearm I handled...I learned it inside and out...I could strip it down and reassemble it in total darkness and when I returned to civilian life, I wanted to own one.
And that's how military rifles become sporting rifles.
There are very few things that man has created who's sole purpose is to kill. The morningstar and the footmans flail immediately come to mind. They have but one purpose. But firearms? They have many purposes and killing is the least used of them all.
When you consider the amount of ammunition expended yearly and the numbers of people killed by those expenditures only a moron, or political propagandist could assert otherwise.