So the question is, on what does their atheism rest?
Their sex drives.
Think about it. The only social causes which can not be tolerated are those that ask us to control our sexual desires. G-d would not be a problem if He hadn't established a proper place for our sexual expression.
That makes a certain amount of sense, though it doesn't explain why they are wasting their lives crusading for "economic justice" when they could be humping non-stop (pardon the vulgarism).
Because the so-called "G-d shaped hole" doesn't go away just because you want G-d to go away. Man is still a spiritual creature. He can pretend otherwise but his behavior will show it true.
Even atheists don't rebel against G-d, they rebel against the Judeo-Christian G-d. They say "If G-d exists, why did He allow the tsunami to wipe out Banda Aceh?" They automatically presume a good G-d like the G-d of Abraham. They don't presume one of the capricious gods of Rome and argue against him.
They know exactly who they are running from. What they don't know is the love that awaits them if they would only stop - a love that is better than sex.
Shalom.