Well, feudalism and monarchism weren’t “bad” either. Slavery isn’t like any of those because it requires the removal of agency on groups of people. I agree on your point about socialism though. I don’t believe it’s the savor that societies need, but I definitely think some aspects of it are extremely important for a civilizations survival.
I’d argue it’s the savior we currently need- America has gone too far into capitalism, if it were more like the nordics then the empire could have lasted another dozen generations. Though I’d also argue that feudalism and monarchism are similarly bad for the same reason we agree slavery is- it takes away agency of the people.