Christians often impute a fanatical belief in some doctrine -- evolution, the non-existence of God, and such -- to atheists. This strategy presents atheists as hypocritical for condemning religious fanaticism but are themselves guilty of the very fanaticism that they themselves condemn when atheists deny the existence of God, assert the truth and viability of evolution, and so on.
The phantasm of "atheist fanaticism" can be easily explained. Christians assert beliefs x,y, and z in a firm and unquestioning manner. Considered from the point of view of the Christian, if someone does not share in those beliefs, then that someone when he continues to not share in those belief so passionately held by the Christian, appears to be as fanatical of his or her beliefs as the Christian. In other words, the so-called "atheist fanaticism" is a self-misunderstanding on the part of Christians.
I'm sure there are unhappy misguided individuals out in the world, who have unplugged "the existence of God" from their beliefs and inserted "the non-existence of God" without any softening of a previously learned hard-edged fanaticism.
An inability to accept one's own failures generates the phantasm of "atheist fanaticism." Since it is impossible for a good Christian to admit that his reasons for belief are less than perfectly persuasive to other people, a lack of persuasion in his hearers can only be explained by a hardness of heart, and willful disbelief. The Christian explains his failure, in this case, to persuade his hearers to accept Jesus as their Lord & Savior, or in a Young Earth, or whatever, by blaming somebody else for his failures and unhappiness. That his foolish demeanor might explain his failure to persuade his hearers never could never occur to a Christian. Or to speak New Testament: The Christian himself is the millstone impeding belief.
For what it's worth, based on the above, that the proper response to charges of "atheist fanaticism" is something like this: "Black is black. White is white. And gobbledygook is still gobbledygook. That you don't make a very good case is hardly my fault."