The term "religious fanatic" can be applied to anyone whose strength of belief is distasteful to others. One person's saint is another's pariah.
So far as I'm aware, the term is used exclusively as an accusation, a derisive means of saying that the believer has gone too far. As such, they are thought to be at the least liable to twist your arm to win you to their convictions or to be dangerous. Some labeled as such have, in fact, done such things.
But in a society like America, where a person's religion isn't supposed to stick out too much lest it upsets the egalitarian ideal, someone can be called a fanatic simply for taking religion seriously. Those who take St. Francis or Gandhi or Mohammed as role models stand a good chance of being shoved to the margins of society because they don't know when to stop being religious, unlike most citizens who know when to quit in a pragmatic sort of way.
I thought of this phenomenon after reading a description of the Muslim Army major who shot 13 soldiers at Fort Hood. A military investigation found, among other things, that he "exhibited a single-minded fascination with religion that was inappropriate for an Army officer and one that intensified over time."
The report, highlights of which appeared in the Boston Globe, found lots of alleged connections between Major Nidal Hasan's Islamic beliefs and his mental terrors. Perhaps they were the deciding factors and deserve to be underscored. But since when does "single-minded fascination with religion" by itself exclude anyone from being a military officer?
You could argue that taking any of the major religions seriously instills an aversion to warfare and violence, though St. Ignatius was a soldier and an officer, as were deeply committed members of the military during the Second World War.
Does the cap on one's religiousity apply as well to Christians or only to Muslims? The armed forces have been well supplied by evangelical Christians, for example, and many of them would seem to be candidates for exceeding proper standards, just as others routinely collect DUIs.
How do we know when we've crossed into the land of sack cloth and ashes? When a public official will issue us a first warning? Or whether we're no longer considered regular guys?
The Army report's finding re: Hasan's religion is unlike anything I've ever seen before. It creates the potential for depriving believers of their rights.
Major Hasan may be the poster boy for Islanmic fanaticism, as the investigation seems to conclude, but even in his case the term takes on that eye-of-the-beholder ambiguity. They know he ardently identified with his Muslim tradition and sought to address themes related to Muslims in the military. It seems likely that certain extremist elements got mingled with his Islamic beliefs and perhaps corrupted them. But all the report cares about is that he was over the top in his devotion to -- what else? Islam.
In other words, he is guilty by virtue of his adherence to Islam and that makes him, in the report, a religious fanatic. That introduces a dangerous new yardstick that would target those judged to have overdosed on religion.