To return to the case at hand: the decline of lynching may be an improvement in one area, but you have to weigh it against the explosions in the imprisonment and illegitimacy rates, the total societal collapse of a demographic that makes up over a tenth of the population, drug abuse, knockout games, and so on.
Do you think there's a causal connection between the decline of lynching and the various ills you've listed?
How is causality relevant? The absence of continuous general increase is enough to falsify the Whig-history hypothesis, given that the Whig-history hypothesis is nothing more than the hypothesis of continuous general increase -- unless we add to the hypothesis the possibility of 'counterrevolutionary' periods where immoral, anti-Whig groups take power and immorality increases, but expressing concern over things like illegitimacy rates, knockout games, and inner-city dysfunction is an outgroup marker for Whigs.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.