No by your standard there should be much less violence.
That's not how proof works. We have no idea how many carry. There's no evidence that they are more or less safe and it's only one schoool.
That's hardly proof of anything either way.
Violence come in many forms. Not all violence deserves a response with the threat of deadly force.
Remember, we are talking about the type of violence which can only be dealt with through the use of deadly force -- the taking of a life to save the lives of others -- like would have been used against the assailant at VT.
In your world, every time two guys get in a mutual combat fistfight someone should start waving around a firearm threatening to shoot the next one to take a swing.
The threat of deadly force is a serious thing. You go to a class and learn when,
and when you can not, display a weapon and threaten to use, or actually use, deadly force. Brandishing a firearm can have serious consequences if one does not consider all aspects of the situation. People with CCWs go through a far more rigorous background check that when a person merely goes in to purchase a firearm.
The fact that UNC has no more violence, or any less violence, than any other campus is of no value whatsoever. The fact remains that there are armed students at UNC who are not causing any mayhem and, if the need should arise, they may -- MAY -- ba able to quell the type of violence that was visited on VT and save some lives.
UNC has fire extinguishers in the halls and classrooms. They are there just in case they are needed. Everyone knows where they are. There is no guesswork on where they are.
UNC also has armed students in the halls and classrooms. They are there and they may someday be needed. No one knows who they are so anyone intending the type of violence that was visited on VT will have to keep guessing where, and whom, they are.