Definition of Fundamentalist Atheist

Fundamentalist atheist is defined as an atheist with a rigid, intolerant, and dogmatic adherence to atheism or an atheistic ideology. The theory behind this definition is that there exists a fundamentalism which is atheistic and which atheists adhere to much like some Christians adhere their own fundamentalist Christianity. The label fundamentalist atheist tends to be used interchangeably with militant atheist, new atheist, and antitheist.

The labels "fundamentalist atheist" and "atheist fundamentalist" are used pejoratively as a criticism of contemporary atheists by associating them with religious fundamentalists who are intolerant, militant, oppressive, and anti-democratic. Critics of atheists only employ the label fundamentalist atheist as a means for discrediting atheists, not as a way to provide an objective, neutral description of some phenomenon.

This is demonstrated by the fact that you need some sort of ideology in order to be fundamentalist but an atheist — even when defined narrowly as one who denies the existence of gods — is at most referring to a single belief, not to an ideology. If atheism by itself cannot be an ideology, then it cannot possibly be fundamentalist no matter what sort of attitude an individual atheist may have.

Useful Quotations

"Passion for passion, an evangelical Christian and I may be evenly matched. But we are not equally fundamentalist. The true scientist, however passionately he may 'believe', in evolution for example, knows exactly what would change his mind: evidence! The fundamentalist knows that nothing will."
- Richard Dawkins, "How dare you call me a fundamentalist"

There is, however, a need to remember that militant or fundamentalist atheism, which seeks to overturn religious belief by force, is as dangerous as any other form of fundamentalism. Atheism's most authentic political expression thus takes the form of state secularism, not state atheism.
- Julian Baggini, Atheism: A Very Short Introduction

In the broad version of atheism, people simply do not accept the basic premise of theism; in the narrower and more determined position, they believe that the theistic position is not only misguided but actively wrong. Sometimes this is called 'fundamentalist atheism'. (The concepts of fundamentalism and atheism should not really be mixed but critics and theistic apologists like to label the extreme end of atheism as 'fundamental'....)
- Nick Harding, How to Be a Good Atheist