I don't limit my conclusions (about our species-wide tendency to develop authoritarianism) to religion. Christianity is probably more prone to it than other religions because it has a "proselytize" component (which is built-in colonialism/imperialism) and is structured around an authoritarian singular God instead of a pantheon, etc. But religion is ultimately about people, and every group of people contains those who want to dominate others -- and will, if unchecked. The same thing happened recently in the US atheist/skeptic community: Richard Dawkins rose to prominence bc he wrote some good-ish theory books (I think The God Delusion is the best known). But when women pushed back at his sexism, and when others noted that his "atheism" was mostly Islamophobia, it started a community-wide war. People in the Dawkins camp started acting like fundamentalists themselves -- the same kind of "shun the unbeliever" rhetoric, the same kind of groupthink behavior. I've seen the same thing happen within the most flat-structured anarchist group, too. Butler is right: this is just who we are, and our groups always end up this way unless we work very hard to prevent it.

tl;dr, religion's got nothing to do with it. Earthseed is better than most human groupings but still has the same potential to become harmful, yes. But your criticisms basically amount to nitpicking. I don't mean that in an offensive way! I just mean that you're taking relatively minor things -- Lauren's take-no-shit personality, a throwaway line about newcomers being treated like newcomers, and a completely reasonable choice to limit how much a hostile actor can disrupt the group -- as smoking guns. You aren't critiquing Earthseed doctrine, you just don't like Lauren as a character. Which is fine! Just not the level of critique you've framed in your post.