Why Is Whitewashing Bad, But Not Blackwashing?

As Barack Obama would say, "Let me be clear." I am not making any judgments here, I am only asking an honest question. Why is 'whitewashing' bad, but not 'blackwashing?' Any one remember the controversy that erupted when Great Wall came out, and Matt Damon was accused of 'whitewashing?'

https://www.theguardian.com/film/2016/dec/07/matt-damon-on-great-wall-whitewashing-i-didnt-take-role-from-chinese-actor

Below is a link to 'The 20 Worst Examples Of Hollywood Whitewashing' and there is also a mention of #oscarssowhite - remember that?
http://www.indiewire.com/2016/02/the-20-worst-examples-of-hollywood-whitewashing-268110/

So, my question is why have I never heard of such a thing as 'blackwashing?' For example, in the most recent Spiderman movie Mary Jane Watson was played by Zendaya (just Zendaya? That's her complete name? Kinda like Cher I guess). Now, in this article (http://www.wildcat.arizona.edu/article/2016/09/blackwashing-in-film-its-a-good-trend) they write, and I quote, "...some angry white folks on the internet are calling 'blackwash.' So, when people complain about 'whitewashing' are they "angry" too, or is it only white people who are angry? They go on to say, "Michael B. Jordan as the Human Torch raises some important questions about the difference between 'whitewashing' and 'blackwashing.' Wait, did I read that right? The difference? They are asking what the difference is between 'whitewashing' and 'blackwashing?' Are they serious???

If I remember correctly, Idris Elba was rumored to play James Bond, correct? Moneypenny has been played by a black woman in the Daniel Craig movies. Jaden Smith played the Karate Kid in the remake, right? My only point is, I do not remember hearing the term 'blackwashing' in any of the entertainment magazines or news shows, but I sure did hear about Matt Damon's 'whitewashing' in Great Wall. Now please tell me where I am way off, but methinks I detect a bit of a double standard here ... or do those only go one way as well?