Why not? If billions of people can be in a religion then surely millions can be in a subreddit with some religion-like properties.
I think there is probably not a clear and useful line between manipulation and moderation. There's no neutral moderation, all mod policies and actions are towards a certain goal & vision for how the community should be. I'm not sure what fake grassroots would be but I think the upvotes and awards account for that: people know what will be rewarded and the rewards turn posting into a performance.
Anyway I'm going to point this out again because it's useful and interesting: HN behaves in these same ways to about the same degree as any large sub does. The alignment on etiquette, culture, accepted belief and punishment for deviation from it is very strong here. This indicates to me that this is somehow an emergent characteristic of large self-selecting online communities.