Of course atheists are thankful, just ask one. I’m sure he or she could come up with things they are thankful for. What I wonder is, “why?” based upon their own worldview.
For instance, think of all the things that people are normally thankful for, things like food, sunshine, rain, green grass, water, and the physical aspect to life we all take for granted. For the atheist all of this is a purposeless, meaningless, accident. It all just exists somehow, but there is no one (they believe) to thank for any of it. The universe, the world, everything just is.
Or think about what most people normally mean when using the words “fortunate” “blessed” or “graced.” Those are words we use to name a providence of sorts. However, for the atheist, whatever happens in life is neither fortunate or unfortunate, it just is. Any meaning he attaches to an event (or non-event) or state of affairs is completely meaningless and not true in the sense of sincerely believing the “meaning” is an accurate description of anything outside his own mind. Thus any attached meaning of being “thankful” to an event or state of affairs is ultimately pointless.
Consider even our relationships with others. Most people are indeed thankful for friends and family. We are especially thankful for the kindness of a stranger. But for the atheist our relationships are constrained and programmed by the “selfish” gene so that what people do for us is simply a calculation of sorts and is all done ultimately for selfish reasons tied to surviving. This would of course destroy any reason to be thankful for what others do for us and indeed would cast suspicion upon all relationships.
What about at a simple personal level. Most of us are thankful we are employed, were able to obtain an education, and whatever success we may have arrived at we attribute to many factors beyond our control. For instance, none of us had a say as to the family we were born into, what country or ethnic group, or a myriad other webs of connecting circumstances and influences. Therefore we rightly note how thankful we are and how it might have been otherwise. This is summed up by the proverbial “There but for the grace of God go I.” But how would this sensibility fit within an atheistic worldview? For the atheist, all of this is neither here nor there–it just is. Any sense of meaning we attach to it is completely arbitrary and if we were to attach the very opposite understanding it would have no bearing on anything other than our own subjective feelings, which are further reduced in that worldview to nothing more than a pack of neurons firing (Think of Francis Crick). Nice.
So, I guess for the atheist the Thanksgiving holiday is like any other day–he or she simply eats more.