This is the slippery slope fallacy here. Furthermore, echoing TSA's description of the AR-15, a feature of it is its low wall penetration, which would make it a safer option than other firearm solutions. We can say a machine gun is a non-starter because when defending yourself against a potential 50 invaders, you might kill innocents across the street, which is unacceptable.
Also, what if I was a person who lost a loved one in home invasion situation where access to a firearm would've saved their lives? I personally vowed to never let that happen again. Should I be denied access to the most (reasonable) effective home defense firearm?
Now that said, I'm taking TSA's description of the AR-15 in good faith. When I suggested low recoil, low penetration weapons like the 9mm handgun, he said it doesn't have the stopping power. Weapons like the .357 and shotguns, too much recoil and not enough rounds. If there's any kind of objective study out there that demonstrates a firearm that has the same effectiveness as the AR, while being lower caliber and having a smaller magazine, it'd be interesting.