My observations and intuition so far is that, the larger the organization, the more that its injustices outweigh its benefits. Power corrupts, and people always have a way of justifying their own actions to themselves, no matter how unjust or "evil" they may be. As a population, I'm not confident in any one person, or any one small party, to wield the broad authority that a large government has.
I dunno. The more introspective I get the more I think of Oceania in 1984. Ingsoc is purported to be socialist but it's still highly stratified, and the higher classes wield their power in the most violent and dehumanizing way possible. I fear that that's the result of not just socialist organizations, but any organization that becomes large enough.