Nearly all the responses have pointed to a different target. I see now that the OP contains two parallel ideas. By not presenting these as distinct lines of thought readers could not see the link. Because it is subtle I need to reflect on how to best present it, so it can be easily understood and countered appropriately.
Secondly, I did not challenge atheism itself. I have attacked the common and pernicious belief among atheists that all phenomena can be explained in terms of material actions through efficient causes. Thus my sole purpose for the OP was to show that physical reduction and absurdist nihilism must go hand-in-hand. If I have not shown this, I do not attribute this to the weakness of the argument itself, but rather a lack of clarity in my presentation. Clearly, more work needs to be done on my part.
Secondly, I did not challenge atheism itself. I have attacked the common and pernicious belief among atheists that all phenomena can be explained in terms of material actions through efficient causes. Thus my sole purpose for the OP was to show that physical reduction and absurdist nihilism must go hand-in-hand. If I have not shown this, I do not attribute this to the weakness of the argument itself, but rather a lack of clarity in my presentation. Clearly, more work needs to be done on my part.