What it was not is a characterization of a 'racist America'. It was the act of a lunatic.
Assertions of collective guilt is un-American.
Only when they’re directed against blacks are they considered illegitimate. Such as making note of crime statistics, and other negative statistics which disproportionately affect blacks. It’s perfectly fine in America to ascribe “group guilt” to whites, even if the actually guilty whites were a small cohort which has been dead for over a hundred years, and a significant number of whites of those days paid with their lives on behalf of blacks and the abolition of slavery (putting aside the question of what the war may have actually begun over).
And don’t forget “white privilege” in which whites are guilty for being born white, even if to a member of a dirt-poor family in deepest Appalachia.