The appropriate question for somebody who believes in moral progress is, I think, What is the moral equivalent of a Saturn V rocket or a 747? Technological progress is obvious.

Bear in mind that the mass adoption of technology often lags well behind the development of the scientific principles it uses. We're not all flying around in rockets; or even jet planes on a daily basis. Mightn't we expect something similar from moral progress? The fact that some idealist has proposed a moral principle isn't the same as it being generally adopted.

The Saturn V rocket is from the '60s. What sort of moral progress in our society might have reached some sort of critical mass around then? Maybe something to do with this guy or even that guy too? The idea that members of social minorities should expect equal access to public goods, and equal protection against violence, was not a new idea in principle but it was a new implementation in practice (and one still being worked on).