So they once fought under the guise of religion, until they determined it no longer best served their interests.
No, these were mostly different people than the 1917 revolutionaries. Getting rid of religion was not a popular move by the Soviets, which is why Stalin had to quit persecuting it during WWII.
The Trans-Siberian Railway wasn't even completed until 1913. But more than that, such organized oppression and surveillance required advancements in mechanized warfare and communications not really seen until the 1920's. It just wouldn't have been possible for the Tzars to keep surveillance on their rurual poplations in the same manner the soviets did. The tyrannical regimes of the 20th century wern't any worse than those of previous centuries...they were simply more capable.
The 1920s was when the West (mainly America) made its advancements. Russia still remained very primitive until Stalin's 5 year plan. Stalin created his totalitarian reign through making a society of paranoia, a very similar effect in the Spanish Inquisition. He encouraged people to turn each other in, or encouraged the population to spy on each other. He didn't kill the majority of his people using new technology, mostly guns or forced starvation. New communication might have been used by a few rich "inner party" members, but the telephone and telegraph existed even before 1900, and could have been misused by the later czarist authorities.
My point is that religion is not the cause of all the world's problems, it's certain people in religion. Not every atheist is a Stalin and not every Christian is a Torquemada. It's when a certain dogma rises to power in a government that it becomes very vulnerable to corruption.