Actually, I know a number of atheist marines... 3 to be exact.
But would any of the 3 atheist marines that you know allow themselves to be used as a tool of some anti-religion group by filing papers to try to force the USMC to recognize an Athiest group alongside other religious groups and get athiest "chaplains" to lead them in their athiestic religious observations and ceremonies? At the risk of speaking for the KG9 Kid, from the context of his post I inferred that he was asserting that this type of activity -- not one's choice to be an athiest -- is the type of thing that would get you an ass-whupping in the Marines.
I so mean to express that a Marine petitioning for his Atheist club on some US Navy bulletin board at the chapel is going to get squared away like a big dog.