Hmm.. so the Atheists Who Want To Blame Christianity For The Evils Of Communism have shown up?
It's hardly surprising that insane totalitarians would go to war against something that threatens to potentially, let alone actually, be a power structure they do not control. But I don't see this as a product of atheism. They would ideally, I think, want a religion under their control, as the Russian Orthodox Church increasingly seems content to be. The Nazis weren't atheist, but they sure as hell didn't tolerate any Christians letting Christianity get in the way of Nazism.
But if they can't create a religion, and can't find one willing to knuckle under, sure, they'll throw stubborn religionists on the same pyre as all the other dissidents.
Big-C Communism, ie Marxism-Leninism, aka International Socialism, etc - basically is itself a religion, though one that denies that that's what it is.
It's an atheistic religion, and is openly hostile towards Christianity.
That's the thing - the Communists weren't just people who didn't believe there to be a God. They were people who were actively wanting to exterminate belief in God,
especially Christian belief in God.
The deal the Soviets made with the Russian Orthodox Church was a matter of pragmatism on both sides. Lenin and co weren't insane enough to think they could make all religious belief go away just by snapping their fingers. But make no mistake, their long-term plan was a world with no Christian witness at all. Marx actually wrote a poem about wanting to chain all mankind to himself -
and take them all down to Hell!
Yes, he said that. Think about it.