More campus security officers would have reduced violence during the Virginia Tech shootings. This is because of the fact that security officers do just that, provide additional security. With additional security on the campus, there would have certainly been a result of reduced violence during the Virginia Tech shootings because of this.
The statement 'more officers' is ambiguous. Assuming that the campus could use another 5 officers, would that have made a difference? I don't believe so. Active shooters are often not swayed by security of any level, as we saw at the naval yard. If a person is determined to get a double digit body count, that is likely what will happen. Semi auto weapons can create that in a matter of seconds. There is no security reaction to that situation that could stop the immediate threat. More officers does not mean safer.
In every single story I have read about school shootings, something could have been done to prevent it. Counseling for the student, removing access to weaponry, ending the bullying that lead up to the violence. The problem won't be solved over night and it has many sides that need to be examined but some things are just common sense. And more guards is not the answer, it's a blindfold to the true problem.
What we have to do in the United States is make access to guns much, much harder and improve the quality of mental health care. This has happened too many times now, and I'm tired of hearing excuses. Violent people kill people, sure. But they are much more dangerous with guns. Obviously.