Well, most of the general public can plainly see that a wingnut psycho with an AR-15 and a stack of thirty round mags is many times deadlier than a wingnut psycho with a bolt action rifle or a typical handgun. Until those in the avid assalt rifle camp recognize and respond to this simple fact, this debate will continue in the same polarized circle jerk vein. There's plenty of fault on both sides, I'm just saying.
You clearly didn't view the website above. Virginia Tech, which remains the deadliest mass shooting in the US, was committed with two "typical" handguns and a stack of 10 and 15 round magazines. Not including Sandy Hook, here are the 10 deadliest shootings in the US thus far...
1. April 16, 2007 – Virginia Tech campus in Blacksburg. 32 students dead plus the shooter. << Glock 19, Walther P22 (pistols) with 10 and 15 round magazines.
2. Oct. 16, 1991 – Luby’s Cafeteria in Killeen, Tex. 23 dead plus the shooter. << Glock 17, Ruger P89 (pistols).
3. July 18, 1984 – McDonald’s restaurant in San Ysidro, California. 21 dead plus the shooter. << Uzi carbine, Browning HP, 12-gauge Winchester 1200 (semi auto "assault weapon", pistol & shotgun).
4. Aug. 1, 1966– University of Texas at Austin. 16 dead plus the shooter. << too many weapons to list, but primarily a shotgun and a Remington hunting rifle
5. Aug. 20, 1986 – A post office in Edmond, Oklahoma. 14 dead plus the shooter. << Two Remington-manufactured M1911 (.45 ACP) Semi-automatic Pistols, One Ruger (.22-caliber) Semi-automatic Pistol.
6. April 20, 1999 – Columbine High School in Littleton, Colorado. 13 dead plus two shooters. << Intratec TEC-DC9, Hi-Point 995 Carbine, Savage 67H pump-action shotgun, Stevens 311D double barreled sawed-off shotgun (and 10 round capacity magazines). Debatable if any of these weapons qualify as "assault weapons".
7. April 3, 2009 – Immigration services center in Binghamton, New York. 13 dead plus the shooter. << 9mm Beretta 92FS Vertec Inox, Beretta Px4 Storm .45 caliber (pistols).
8. Nov. 5, 2009 – Soldier Readiness Processing Center at Fort Hood, Texas. 13 dead. << FN Five-seven pistol, Smith & Wesson .357 Magnum revolver.
9. Sept. 6, 1949 – Camden, New Jersey. 13 dead. Howard Unruh, 28, killed neighbours while walking near his home. He never went to trial; he was determined to be a paranoid schizophrenic. << Luger P08 pistol (a single handgun from WWII).
10. July 20, 2012 – movie theatre in Aurora, Colorado. 12 dead. << Smith & Wesson M&P15 rifle, Remington 870 Express Tactical shotgun, 2 Glock 22 handguns (as far as I understand things, the majority of the shooting was done with the handguns after the rifle jammed).
So, as we can see, the majority of these shootings were perpetrated with semi automatic handguns, which are no less deadly than semi-automatic rifles, or "assault weapons". The differences are purely cosmetic.