I feel like I understand communist theory pretty well at a basic level, and I believe in it, but I just don't see what part of it requires belief in an objective world of matter. I don't believe in matter and I'm still a communist. And it seems that in the 21st century most people believe in materialism but not communism. What part of "people should have access to the stuff they need to live" requires believing that such stuff is real? After all, there are nonmaterial industries and they still need communism. Workers in the music industry are producing something that nearly everyone can agree only exists in our heads. And they're still exploited by capital, despite musical instruments being relatively cheap these days, because capital owns the system of distribution networks and access to consumers that is the means of profitability for music. Spotify isn't material, it's a computer program. It's information. It's a thoughtform. Yet it's still a means of production that ought to be seized for the liberation of the musician worker. What does materialism have to do with any of this?
Also, realists (be they Abrahamic or atheist) aren't really capable of accepting foreign religions to the fullest extent. Before the Romans came and fucked everything up, polytheists generally believed in the gods of foreign cultures as well as their own. The Romans used religion as a tool of conquest and said "actually there's only one pantheon, y'all have been worshipping Jupiter the whole time, surprise, now please don't revolt against us". Then they converted to Christianity and said "wait, there's only one god. Polytheism is fake and bad, every other god doesn't exist". Then atheism became popular starting in the Enlightenment, but in a post Rome world atheism existed primarily as a reaction to monotheism from people who didn't understand polytheism or history.
As an unrealist, I believe in all gods. What do I care if they're real, I'll believe in them anyway because it's a nice thing to do. And that's how most people felt about foreign gods before the Romans. But in the post Roman world, you have genocide from Christians who think it's a crime against the lord to be a dirty foreign pagan, and you have dismissiveness from atheists who don't really know the value of a religion because they're stuck in this realist mindset where they can't adopt the beliefs of foreign cultures. And I don't think the Stolen Generations in Australia were primarily religiously motivated, they were realist motivated. Capitalist realists wanted the aboriginal children to be taught about the "real" world, instead of aboriginal communist dreamtime "nonsense". And I don't think atheists are capable of fully understanding the value that's lost when 60,000 years of oral religious history is genocided away. That's a whole world, extinct. That's a whole world extinct for every single tribe that doesn't have anyone to tell its stories anymore. If you only believe in one world, you can't believe in the value lost there.
So I think realism has an important racial component that's often neglected.