Are you sure about that, isn't that why BLM are calling for a different slant on history, from the perspective of the slaves, not the masters. Sorry if I've misunderstood I thought present day history books are being accused of glorifying bad things (as you put it!)?
All History is written from a certain perspective, usually from the point of view of the victors not the vanquished, isn't this why there is now this argument that the story from both sides needs to be written to ensure a balance.
The problem with the 'blanking out' in history something you don't like, or society now finds unacceptable, is that this doesn't change what happened, and worse still it doesn't help to understand where modern day values and/or the pain comes from. 'An eye for an eye' leads to a world without sight and understanding and more than anything ensures past mistakes will be repeated.