If the teacher discussed Kwanza, would she give the complete history and criminal record of the man who started it? In the matter of truth, of course. And let's say her class contained a number of small black children.
She probably would mention that it was a holiday made up by a man in recent years...
But why not tell the unvarnished truth, that Kwanza's founder is a marxist and a criminal teaching college somewhere? Where do you decide enough is enough? That's the point.