When I read the OP I couldn't take it seriously, hence my 'Mysterons' comment. By its nature, the question can only answered by opinions and theories, as we have seen. Some of those opinions and theories have suggested to me that we may be better able to address the question of who is stealing our history (present tense) rather than who stole it.
When someone claims that "Reading The Dark Earth Chronicles helped break the spell, blah, blah, blah," and then goes on to categorise it as a "Mudflood Theory," to me something is wrong somewhere. I recognise that as joint author I am more sensitive about the subject than others, but to me it's an insult. In effect it's a redefinition that brings with it all of the 'baggage' associated with the general mudflood ideology, which has nothing to do with The Dark Earth Chronicles.
It occurs to me that this is exactly what might happen when something is indexed or classified in a computer database. Let's say, for example, an Artificial Intelligence database. With this in mind I have reexamined the other opinions that have been put forward and some of them do have the stench of AI about them.
Artificial Intelligence is based upon information and it's classification, manipulation and comparison. It's not based upon knowledge and cannot employ wisdom. It can construct opinions based upon information, statistics and algorithms, but it has no concept of knowledge or wisdom.
The website I run brings its fair share of correspondence, for which we are very grateful. One contact in particular was highly excited by his discovery of a new AI 'app' that allowed him create videos from whatever text he would cut and paste into it. He sent some examples of videos he had created using text from articles on the website. The text was not reproduced in full, but analysed and a synopsis created which was then matched with what was considered to be an appropriate video clip.
The first attempt used the fairly innocent 'Welcome' page and did a reasonable job.Later attempts taking text from more complicated articles were a disaster. The synopsis produced completely changed the emphasis of whatever point was being made and in some instances produced utter garbage. The choice of video clip was also quite bizarre in some instances. The AI took the information and redefined it within its own specific parameters and algorithms.
My point is that AI now has all of the information it needs to be able to pontificate upon any part of what is classified as 'history' and anyone and his wife can now go and ask any question they so desire without having any previous knowledge of what they are asking about. In return they receive calculated opinions and related information that they can post in a forum or whatever. This doesn't make them knowledgeable, it just gives them an artificially informed opinion and these opinions are nearly always redefined and 'politically correct'. The calculated opinions and related information are always delivered in a language style that feigns authority and is embroidered with unnecessarily complex words in an overly pretentious manner that no one would ever use in normal conversation.
So, who is stealing our history? In my "opinion" it's Artificial Intelligence.