slavery doomed the empire from the start.

That’s the most egregious moral and social flaw but there were others that could also have doomed the US from the start. A lot depends on the culture, how it evolves, and which values and narratives are promulgated by civil institutions.

Compared to 100 years ago, USA is objectively less racist, less homophbic, less xenopobic, and generally more tolerant and respectful.

Especially if you consider USA during Obama/Biden. Racists were still racist but the messaging from the top and most of society was: other races are OK, other cultures are OK, other sexual identities are OK