I had this argument with JBG (and a couple of others) on #forums a week or so ago.
If enough people believe something, then it becomes "truth" (without getting mixed up in semantics and definitions)
Take for example a simple fact we all know is false, such as "the russians landed on the moon first". If all schools educate their children in this, and all literature saying anything to the contrary is changed, then within 2-3 generations people will happily accept that. It becomes the truth.
Game just found
this article on the internet (thanks Game!) where someone has tried to prove this by altering a wiki page.
I can't remember what JBG's exact point was, but he disagreed and said that even if enough people believed it and it was taught and educated to the next generation, it still wasn't truth.
My point is simply that the truth is actually relatively easy to change, within reason. The internet both supports and refutes this - it's harder to control factual literature that exists on the internet, but it also means people can post false information and pass it off as fact.