I suspect there are a couple of different factors in play here. Firstly, there is the fact that, as SP pointed out, though slavery was "abolished" after the Civil War, the attitudes inherent in it were still prevalent in law until the 60s, and are still to be seen socially widely across the States. This is embarrassing to many, particularly in the high profile areas such as NY and Cal. And it is easier to express that embarrassment in the context of history than current affairs. Then there is the "Protestant" background on which the US was founded - for which read a strong dose of religious hypocrisy! There is a strong thread of the idea that "repentance" makes everything right - so you can carry on sinning again. In the UK, the ethich has tended to be "OK, you're sorry, now don't do it again". Perhaps a simplification, but relevant, I feel