noun: a person with an extreme and uncritical enthusiasm or zeal, as in religion or politics.
And nothing new or useful is going to come from this awful tragedy, either. The boring, gross, cliched argument that "guns don't kill people, people do" is already being made. Again.
A friend of mine was shot last January--he's ok because it hit him in the elbow, but he described it as a random, "I got a gun for Christmas" shooting.