Myth:
All atheists believe in "X."
Response:
Although there are a lot of different myths about atheism and atheists, there is one theme which keeps coming up over and over again: the assumption that all atheists share some political position, philosophical system, or attitude. In short, it's assumed that all atheists believe some "X," where X has little or nothing whatsoever to do with atheism. Thus theists try to pigeonhole atheists into a single philosophical straight-jacket, be it humanism, communism, nihilism, objectivism, etc.
By claiming to have identified this belief system, idea, or motivation necessary to atheism, such theists can then proceed to attack that idea or belief and pretend to have refuted atheism without ever actually addressing atheism itself. It is certainly true that atheism can be a part of the aforementioned worldviews or that atheism can result from various motives, but it is not true that they are necessarily connected with atheism or even that all atheists share them.
Not only does atheism fail to imply an agreement with any one belief system, it also fails to imply agreement with any other atheists. My neighbor may also be an atheist, but we might disagree on nearly every single philosophical and social issue imaginable (and, in fact, I can think of a few atheists where such an description may be accurate). Someone who attacks my neighbor's beliefs doesn't address my atheism or atheism itself.
It might help to consider the parallel situation of disbelief in elves: does anyone think that this indicates wider social or political agreements? Just because I and the current pope agree on not believing in magic elves does not announce to the world that we agree on anything else. Were someone to suggest it, they'd be regarded as daft. Similarly, announcing that I disbelieve in gods does not announce to the world that I share any particular beliefs with any other atheist.
Finally, it should be noted that the aforementioned method of attacking something associated with atheism in an effort to refute atheism is a logical fallacy known as a Straw Man. It doesn't matter how awful or wrong ideologies like communism, or nihilism might be, nor does it matter what motivation atheists have for being atheists, or what other ideas might be common among atheists. Why? Because none of this can have any bearing on whether or not atheism is a reasonable position.
In order to argue against atheism, a person has to show that atheism itself is not reasonable and simply ignore the rest. This, however, is very difficult to do, whereas attacking communism or atheists' allegedly "defective fathers" is very easy. Many books have been written which assert that this or that person is a "representative" of atheism and proceed to refuse that person's philosophy or motives as if this were also a refutation of atheism. Needless to say, these arguments fall completely flat because they miss the point entirely. It may even be the case that the authors realize this.
