I think we have to keep two things seperate concerning hoaxes. For one, there are those where their proponents are simply convinced of something, and are trying to convince others, at the same time developing an ignorance to any counter-evidence because the particular believe grows more and more to be a part of that persons identity. I'd like to name that the "mythological hoax", I'll explain later why.
The other kind is people conciously making up stuff, because they realise that people currently are very receptive to that kind of things, and they might be after prestige, a fast buck, the same things frauds and impostors have been after during all of history. I wouldn't even call that a hoax, I'd simply call it what it is: fraud, which, if it leads to material gain of the one responsible, is a criminal offense. The Apollo 20 hoax clearly falls into this cathegory, since you can't possibly believe in it if you're faking your evidence on your computer. I'd file the original moonlanding hoax under the first cathegory.
There *might* be a weird combination of the two, a case where someone is totally convinced of something despite there being any evidence whatsoever, and forges some evidence to gain support to "get to the bottom of it", in a "the ends justify the means"-line of thinking, but I'd say they are pretty rare, since it takes a person with a heavy double morality and absolute conviction to pull it off. Such a combination should be rare to find in a more or less sane person.
Now, why did I call the first sort "Mythological Hoax"? Because I believe that's exactly what it is. The twentieth century robbed the western society of pretty much all mythology there remained from the times of old. First by scientific progress, then by deconstructivism we banned them all to the realm of fairy tales or high literature.
I think the rabid spread of all kinds of conspiracy theories during the last two decades is a compensation for the loss of mythology. Most people need to believe in something different from aparent reality, it seems (and I, having a very strong conviction in my faith, am by no means an exception). While there was plenty of opportunity to find this in the physical realm in earlier centuries, People are now turning to the next best thing they can't comprehend: The confusing, enigmatic world of politics (sometimes combined with the equally enigmatic world of high finances). Surely, there got to be some dragons left in that inpenetrable mess!
In general, myths are located where the power is. A myth isn't of much use if it doesn't affect your life in any way, like, say, that all ballpens you never found again made their way off-world in search for their mysterious home planet (yes, I'm ripping off Douglas Addams...). A myth has to have power, be that in the realm of Gods, the spirits around us, or the politicians governing us.
Think of it this way: Conspiracy theories about global conspiracies, world governement and whatnot are gravely overestimating the power of politics and politicans. No men can control the world, and certainly not history, all too volatile is the substance we are dealing with. Yet, with most people in the west having lost their faith in a god that can make the world right, they have to get their hope for a better world from somewhere else. They take it from politics. Of course, the world and politics are a mess right now, so they have to be evil. None the less, they have to have the power to claim responsibility for it, to controll the whole process behind the curtains. Because if they don't have that power, there's also no hope for someone having the power to do the same in a good way. I hereby suggest that what we see with mythological conspiracies and hoaxes is an emerging 21. century western eschatology.
