I hope he focuses on his individual right to an effective self-defense, rather than trying to get into hypotheticals or statistics about providing some benefit to society.
"How many victims of all these mass shootings were armed and able to defend themselves?
"How many innocent persons have been injured or killed during mass shootings by legally armed private citizens acting in lawful self-defense?"
My right to carry on campus in about my right to an effective self defense. Period, end of story.
If other students choose to do likewise, good on 'em. If enough of us do, that might create a deterrent effect, or provide some other social benefit. But that isn't the reason the RKBA exists. It is about my right as an individual.
At least that is what I think is the most powerful talking point on this subject.