If I was some crazy sot trying to go out in a blaze of glory, and I arrive at that school with ill intent, the first question that should be bouncing about in my mind is how do I really know he is not armed? How can I be sure, and how lucky do I really feel about that decision? This may very well make me decide to opt for another target, and by creating probable doubt in me this brave man has managed to save lives. Crazies, like many predators and scavengers, will tend to home in on what they consider soft targets. Even healthy lions will target weak prey ...even when they have sufficient strength to take stronger prey they will opt for those will obvious injuries/weakness as a way of ensuring success and/or mitigating against unnecessary injuries.
If I was a criminal, I would rather go to a school that doesn't have a Marine/Army/other standing in front of it.
I think this applies for CCW also ...in cities/areas that are known to have a lot of CCW license holders, or for that matter places that have clear Castle Doctrines in place, people tend to more or less be very respectful. Even though, statistically speaking, if I walk up to you and start beating you up there is a high likelihood that you do NOT have a gun on you. However, you MAY have one, and due to that I will most possibly opt to not engage with you (unnecessarily) because of that.
I think that is also similar to SSBNs ..even if you have a successful nuclear first-strike, taking out or operationally disabling your target's ability to respond with his own ICBMs, there is always the thought that - right now - there are several nuclear ballistic submarines moments away from firing their SLBMs at you. You are not sure where they are, you are not sure if they have their full contingent of warheads, or even if they received their orders in time. Maybe your attack submarines managed to sink them. However, you are simply not sure.
If I was a crazy, I'd see this guy standing there. A US Marine (since I take it there are no former Marines). In uniform. A father. Protecting children.
And I have no way of making sure he is not armed apart from what I read in an article.
I'd get in my car and drive on.
This man is doing a wonderful thing.
The "This is a gun free zone" sign might be a hint.
He's on school property. It's against the law to carry on school property. The answer is, he's not armed.