My father was a history professor who specialized in American history. I don't think the author of this post gives sufficient credit to history, historians, and people who teach history. These "shocking" facts, whether they're scandals, little ironies, or just things that contradict our present prejudices, are not secrets. They aren't hidden. Some people will trumpet them more than others, depending on various biases ideological, partisan, national, etc., but nobody is being silenced. The main problem is that it's hard to get people excited about them for more than a few seconds.
One thing I pointed out here recently is that all the "things they didn't you in school" books are populated with exactly the facts they taught you in school. Similarly, all these "shocking" facts here -- will you recognize them if you run across them a year from now? Two years from now? With that in mind, can you be sure that you haven't seen them before? Maybe multiple times? The strongest distortion of history is our limited ability to pay attention and then remember.