Because after you ban the AR 15s kids will start using hand guns to shoot up schools, then you'll push for banning handguns, then they'll start using other weapons and you'll push for banning those as well. Of course you already know this. You just want to slowly remove guns from the united states because your a typical gun control advocating parasite.
First of all, I'm far more centrist on gun issues than most liberals. I'm not an advocate for 'gun rights', but I'm also highly skeptical of the efficacy of most gun regulations. The slippery-slope argument in this post is just par-for-the-course beachbum stuffpost material.
Second, ask yourself this: if handguns are equally viable tools for shooting up schools, then why do so many of the shooters use an AR-15? If they work equally well, why don't we see mass-shooters using different guns at a frequency which is
proportional to the amount of different guns in civilian homes? In other words, hand guns are more common, so why do we see so many of them using AR-15s?