Yeah? Sure that was horrible. Yes it was inexusible. But note a couple things. First, we're one of the few countries that fall over ourselves to apologize for past things. Any apologies from China about its past? Japan? Any one of a dozen countries in the Middle East? Russia? Europe and America have a near monopoly on the Mea Culpa department.
Second, this only shows that America is like any other culture or civilization. Where two or more are gathered, there will sin be also. This shouldn't be an occasion for Leftists to condemn the US as the most evil country in history that needs its foundation stones burned to the ground (though it no doubt will be added to the long list). It also shouldn't be used by Catholics who confuse the Church's warning not to embrace 'Americanism' with the idea that America is the alpha and omega of all suck. Especially given the Catholic Church's recent falls into embarrassing sin and incompetence.
So it shows America has sinners, and no doubt we'll find more dirt over the years.