I think it’s the intent behind it. From what I understand atheists don’t believe in a divine being so them drinking juice and calling it blood wouldn’t be satanic but more so it’d be blasphemous or sacrilegious.

In Christianity, John 6:53-57 explains why Jesus offers wine as his blood. It’s a physical manifestation of the understanding that if Jesus is not within you then you are not saved. It’s not so much a ritual as it is a declaration of one’s belief. It’s not cannibalism either it’s more so imagery to drive home the idea that Jesus is sufficient for a full life and salvation.