Interestingly, slavery was a feature of Utopia as described in Thomas More's original book, which happens to have been written by a nobleman, about 500 years ago (it was published in 1516).

I'm not really making any claims about the utopia-status of our society, I'm merely saying that promises of Utopia are not inherently off-mark; the enlightenment people had a lot of mistakes in their expectations for the future, but overall, their optimism and enthusiasm was warranted (my argument depends more on what counts as a "promise of Utopia", rather than what counts as "Utopia").

It's admittedly easier to find examples of Utopias that went horribly horribly wrong (especially in the past century), but when something went right for a society, you can find people that were working towards that goal; the US founding fathers are another example, at that time, nobody expected the US to succeed as a republic (the established wisdom was that democracy may sometimes work for small city states, but of course it could never be functional for a large country).