Hardly: the French Revolution was first (to my knowledge) manifestation of politicized atheism in history.
I am not trying to idealize religion, or whitewash the history of Christian civilization. I'll be the first to say that religion-based morality is deeply flawed, resting on a contradictory heap of taboos supported by nothing but the illogical appeal to authority.
But it is a morality, warts and all. Just as LowDown says, a barrier - however imperfect - to wholesale slaughter of innocents.
Put yourself into the shoes of an uneducated, simple Russian soldier in 1917. Everything is falling apart. The monarchy is gone; the war (unimaginable, bloodiest war ever, without reason or purpose) is lost - yet somehow never ending; out of sudden, there are hundreds of parties and groups, each claiming that their way is the best way...Your confusion is approaching its theoretical limits.
And one group in particular is making a remarkable claim: they have discovered the root of all evil: there's a "class" of people among us, hiding in the plain sight, that is blocking our predestined march toward beautiful, fat, pain-free future, and causing all the suffering. Get rid of them, every single one - and things will change.
What do you have to lose? "Only your immortal soul" - the priest says. But if there's no such thing as "immortal soul"...