Well, there are probably other ways to do it, Fuzzybuddy, if you think hard enough, but basically you're right. The automatic weapons certainly make it a lot easier.If your dream is to be a great serial killer, all you need is a pair of hands; but to be a great mass killer , you need an automatic weapon.
I have never yet heard any reason on earth that anyone (outside of the military) would need or want an automatic weapon, unless they want to be able to kill as many people as possible. Which certainly is mental illness!