Originally Posted by CheeseForSteeze
No, it doesn't exclusively. Anything can be mastered as a deadly weapon and a semi-auto rifle is no different in that it requires more of an investment in training than the media and entertainment have misled the population to believe to be deadly. Anyone who is a firearms hobbyist will tell you this.
I have friends that study Japanese history and many of them are kenjutsukas of decent skill; decent in the absolute scale of mastery relative to samurai. They are more than skilled enough to use a katana or any large knife and cause havoc worse than most of these shooters given the adequate preparation and willingness to die for the "cause". Luckily, they're just harmless video game nerds that would only use lethal force if their lives were in jeopardy.
Pure and simple casuistry. You're choosing one highly irregular example and applying it as a general rule.