Religion remains, I believe, the number 1 obstacle for communists. I read that in Russia, the main group that fought back against them were religious groups. And communist China learned from this, so they went super hard against the religious right away and shut them down with extreme prejudice. Then you look at what they've done in the USA, extreme amounts of propaganda aimed at turning people away from religion for decades now. The human heart is built for religion, and frankly you may call it supernatural, but God does let you know he he's listening if you pay attention.