How about this angle? Did you ever notice these shootings all have another common feature? They're all in "gun free zones" where responsible, competent gun owners are disarmed so they can't do anything to help.
You say only the police and military should have guns but you don't take into account the fact that banning guns won't keep them off the street since there are MILLIONS of them out there that are unregistered and untracked in the hands of people that would love to have you make sure their victims are unarmed and unable to defend themselves. With the police and military having guns now, they didn't do squat to help anybody, so why do you think it will be different? Banning guns simply makes sure that law abiding citizens will be unarmed.
It's illegal for someone without a driver's license to drive a car, but it doesn't stop them. It's illegal to drive drunk and yet over 10,000 people a year die in alcohol related crashes. I don't hear you banning cars though, or even petitioning for alcohol sensors as a legal requirement. How about banning alcohol? Oh, right, prohibition proved that banning something doesn't make it go away.