There is one sense in which the US has noticably regressed. Back In The Day we wrote on the Statue of Liberty "Give me your tired, your poor, your huddled masses yearning to breathe free." Then in the had a big panic about foreign terrorists in the early 1920s[1], which ended up with the US cutting back on immigration by more than an order of magnitude. The recent panic about foreign terrorism certainly isn't helping, either.
I think the best sentiment is that we should go back to how things used to be in areas where we've regressed (immigration, human rights, limits on the power of government, etc.) but stay where we are in areas where we've progressed (racial integration, voting rights, overall prosperity, cleaner industry, etc.).
I think the point is, ethical progress (be it through abolition of slavery or greater tolerance of difference) should lead to a greater positive effect on the status quo.
If other forms of social, economic and political injustice take the place of previous abominations, the net result is a state which appears disinterested in positively affecting its ethical standing on the world stage.
There have always been ugly things about the country - just like pretty much every other country, if you dig some.
Not to say people shouldn't point out the defects and work to improve them, just that hand-waviness isn't part of the solution, IMO.