I read through the responses and I didn't see any (sorry if I missed) addressing the REAL reason I think everyone should be able to carry on campus. I don't fear much for the lone shooters who take out places like Virginia Tech. They're few and far apart. While an armed student could possibly stop a thing like that, it's a spaghetti plate of hypothetical guesses. While those incidents are tragic, they are thankfully too rare to be statistically significant in terms of personal protection and your actual chances of being involved.
No sir, what I worry about is walking down a half-lit campus street with no recourse to muggings (or rapes, should you be of the fairer sex) other than sprinting to a blue-lit phone and hoping the police get there before it's over. The commonplace muggings, assaults, and rapes on campuses need to be addressed. Think like a criminal: Where do you seek a victim, at the shopping mall parking lot or the campus parking lot? Lots of classes run until 8-9 PM, and predictably unarmed students disperse into the dark every night of the week. If I were looking for $5 for my next crack rock, I'd be sitting in one of those school parking lots with a baseball bat and a plan.
These every day crimes don't involve people being used as backstops the way the OP described the situation. It's you and bubba, all alone - may the best armed win.
Sharp as a cue ball...but moving faster.