A big part of it, I suspect, stems from the realization that our history is largely whitewashed to cut out the less-than-noble events... now this is nothing new, of course -- every culture writes its history to its advantage; how else do you preserve nationalism? But there's an understandable backlash -- people who realize they've been lied to become suspicious... some of them take it to extremes...
I have heard of the less than noble events all my life, and I'm old. You hear some aspects more than others of course, and then you learn good and bad things as you get older. Sadly, today we can't grasp that at times when you look at history you must also deal with the mindset of the majority at the time. People can't seem to do that, and claim its justification for a understandable backlash.
You do use the mindset to a point in order to grow, and progress a human beings. When do people acknowledge that is part of progress? Sadly, today I don't think they wish to be capable of that. It seems they just wish to be angry instead, and I don't understand that at all.
Its part of the process of being human.
If all we wish to do is hold things against dead people of the past, because they felt - with good intentions most of the time - that was part of keeping things together in the best way possible? Than you will have nothing in the past, and no good humans that did things to advance this country - or any country for that matter - to learn from and advance from their ideas. Pretty soon you will be isolated, because humans fail all the time. It's the nature of being human.
I remember some of the junk that schools pumped into us as children, and its pretty much laughable at my age now. It was deemed the 'think to do' at the time. I remember NOT buying it 100%, and I know many of my friends that felt the same way. We laugh about it now, and acknowledge our gut was right. Yet, to be more modern I suppose I should label them, stereotype them, yell and feel angst towards them. I know the purpose now, and I place it in context. I still don't agree with their decisions, but at that time in history I can understand WHY they did it that way. lol very though I still think it was stupid!
I suppose if people wish to get angry and resentful they can, but to call it understandable? I'm not sure I can go that far.