Rational doesn't mean "thinks like a typical person" (or more often "thinks like me"). Rational means "able to follow some consistent set of rules". All politicians are rational (just highly self-centered).
Wanting a place on a scoreboard is one possible value that allows mass shootings. Another is feeling wronged by "normal" people, or people associated with some particular group, and seeking revenge. If the media didn't make up the "what's your religion? Christian?" thing, this shooter also exhibited the latter.
What else does a gun imply outside of a gun range, hunting ground, or in the hands of police officer?
Provided that you aren't miles away from civilization? Merely an inflated hospital bill, at least in America. But that's a different problem.