Militant atheism is often used as an implied anti-atheism put-down. Although it is arguably an accurate description in certain cases for a particular interpretation of the word "militant", that word also carries with it a number of other associations which are definitely not true.
- vigorously active and aggressive, especially in support of a cause: e.g. "militant reformers"
- engaged in warfare; fighting
The first definition is arguably applicable to the most active or assertive defenses of atheism, although "aggressive" carries with it a further implication of physical aggression -- which is definitely not the case for any but a few isolated atheists, and definitely not a part of the mainstream atheist community.
The second definition, however, does not apply to any known atheists -- at least, not in the sense of being engaged in warfare (other than verbal) about atheism. (There are certainly many atheists involved in warfare -- as soldiers or freedom fighters, for example -- who might therefore literally be described as "militant atheists", but there are no known instances of the phrase being used in this sense.)
In short, then, the primary definition carries with it some negative connotations that are untrue, and these connotations are further reinforced by the second definition (which is completely inapplicable).
The phrase is most commonly used as criticism of any attempt to rein in religious extremism, e.g. by subjecting speech from religious professionals to truth in advertising standards or preventing individuals from acting on intolerant religious beliefs where said actions would conflict with the ideals of a tolerant society (see tolerance of intolerance).
- "Actually, I'm a militant pacifist."