Well, yeah, sometimes it is.
Unfortunately, though, just because a person is an atheist doesn't mean that everything they do and say is rational.
For a while there it seemed to me that there was absolutely no reason to think that atheists, as a whole, were more rational than religious believers, but then I reminded myself that my observation is limited to the behavior of a small number of people, and that, like everyone else, I select what I pay attention to, and that I focus on atheists who are dumb. The reason I focus on them is because it seems to me that many atheists are not practicing nearly enough self-criticism, neither of themselves nor of other atheists. If you're not stupid already, just assume that everything you say and believe is factually correct, and you'll become stupid soon enough.
In addition, not everyone who is an atheist announces it all the time or puts it in large all-caps at the top of their Facebook page. It may very well be that the average atheist who announces his or her atheism very aggressively is less intelligent than the average of all atheists. It may be lately that some of the more intelligent atheists are announcing it less than they used to, because the thought of being associated with dimwitted, agressively-atheist atheists embarrasses them.
Sometimes I'll say something like "not everything an atheist says or does is necessarily rational" to someone who's said something like "ATHEISM IS RATIONAL!" and they'll agree with me. And if all they meant is that skepticism of religious belief, all other things being equal, is more rational than belief, then I agree with them.
Other times they'll get hostile.
It may happen that a person who is as atheistic as anyone may ask when Jesus died, and someone may reply that Jesus never died because He never was born and that the Bible is completely fictional. In such as case, sometimes it turns out that the person saying that Jesus never existed means that the supernatural things related in the Bible never happened. In that case, I agree, but wonder when the word is going to get around that some of us occasionally discuss a completely non-supernatural Jesus. If by saying that Bible is completely fictional, someones means no more than that they have no belief in the supernatural, well then I'm sorry, but I think they expressed themselves unclearly. The Bible is studied by quite a few people who have no belief whatsoever in the supernatural, and there is quite a lot of historical content alongside the tales of the supernatural. How much historical content?
That's exactly what we're discussing, a lot of the time: how much history the Bible contains. And the reason that it's such a significant topic is because for many historical topics, we currently have few or no written sources other than the Bible. Completely ignore what the Bible has to say, and you've chosen to completely ignore centuries' worth of the history of large areas of the Middle East. Yeah yeah yeah, we know, you don't believe in the supernatural, neither do we, we're talking about something else now, is how we often feel when you interrupt our conversation because you think we believe in God. And you know what? Sometimes some of the people in these discussion do believe in God, but everybody understands that we're discussing something else at the moment and everyone's discussing it rationally.
By the way, discussing how much history a written work contains? That's exactly the same thing we often ask about works written by historians. We don't consider anyone to be infallible, not even historians, not even *gasp* scientists. (Not even atheist scientists.) We question everything. Everything.
Where was I? Ah yes: atheists are rational. Yes, occasionally we are. I often try to be. In spite of constant misunderstandings.