Strictly speaking, there is no such thing as collective memory--part of the same family of spurious notions as collective guilt. But there is collective instruction....What is called collective memory is not a remembering but a stipulating: that this is important, and this is the story about how it happened, with the pictures that lock the story in our minds.
Although distortion of the past is widespread, the most common travesty is one of omission, wherein populist leaders neglect to mention the crimes committed by their own side or recollect them in such a way that evades accepting full responsibility. That politicians are so able to evoke historical arguments in these ways results from a prior failure of the society to engage in a full and frank encounter with past wrongdoings.
In terms of the Internet, it's like humanity acquiring a collective nervous system. Whereas previously we were more like a [?], like a collection of cells that communicated by diffusion. With the advent of the Internet, it was suddenly like we got a nervous system. It's a hugely impactful thing.