Stalin's grip wasn't absolute either. We still know about Trotsky, despite his efforts. That doesn't mean the censorship didn't have very real consequences.
What "very real" consequences did Facebook have beyond its platform?
Stalin only had control over the speech and thoughts of around one hundred million people in one country.
Zuckerberg has control over the speech and thoughts of around three billion people in countries across the world.
That's ridiculous, Zuckerberg has control over neither.
Does my cellular service provider control my speech and thoughts?
Does Microsoft control my speech and thoughts because I use Windows?
Does the Post Office control my speech and thoughts because they collect and deliver the mail?
No, no and no. I don't think you understand what the word "control" means.
You don't think communication influences or directs people's behavior?