How do you plan to handle the inevitable invasion of Holocaust deniers, Nazi apologists and so forth? For example, the accepted answer to a question about WW2 Why did Hitler declare war on the USA? links to the webpage of an institution widely accused of skewing the history of WW2. Yet the author of the answer treats them as a trustworthy source.
Yes, I think that this is a big problem. Consider this answer for example, 5 people apparently found it useful. Yet it lists very strange "facts" that aren't confirmed anywhere (in fact, you can easily find sources that say the exact opposite). I noted the issues and got "are we trusting KGB now" as a reply - conspiracy theory at its best.
This example shows that relying solely on the community to sort such things out will not work. Some arguments sound convincing enough to collect some upvotes - but that doesn't make them reasonable. And leaving such answers around, with upvotes and even accepted (because the OP is into conspiracy theories himself) will undermine any respect that this site might gain.
I think that we should flag such answers. Indeed, I've done that with the following explanation:
Conspiracy theory - listing "facts" that contradict pretty much all the sources available, not willing to share any sources that support these statements.
While requiring sources for everything might go too far, we should definitely ask for sources when we see statements that aren't obvious or common knowledge (meaning: not verified by a simple Google search). If the author doesn't comply within a day or two we should flag the answer for deletion.
It would be nice if we could automate this process, e.g. have a flag "sources missing" that would add a comment "Your answer makes claims that aren't supported by any sources, please edit it to add them". And that flag would only show up in the moderation queue after two days, to check whether the author complied. But for now the manual process should do as well.
H. L. Mencken said: "the trouble with fighting for human freedom is that one spends most of one’s time defending scoundrels. For it is against scoundrels that oppressive laws are first aimed, and oppression must be stopped at the beginning if it is to be stopped at all."
Let them ask questions and let us respond with facts and references. Let us show with reason why they are wrong.
Asking about why some people consider the holocaust to never have happened would be a grand question -- but would need to be carefully crafted to avoid being inflammatory and comply with the rules.
Note that some of those questions may fall foul of acceptable terms and conditions of stackexchange. I do not think that racism is addressed as such but we should contact the legal team first and foremost. Note that denying the Holocaust is illegal in a few countries and that would be covered by the above terms.
PS: Just to make sure that everyone knows where I stand: Holocaust deniers and Nazi or Communist or any totalitarian ideology whatsoever apologists are wrong and scum. But since I believe in freedom of expression (silly me?), they should have the right to babble nonsense as long as I (and hopefully others) can tell the world that they are wrong.
Let's make sure we under exactly what "revisionism" is. Revisionism is in fact the perfectly legitimate academic process of questioning and, well, revising existing interpretations of the past based on an intellectually honest assessment of new information that has come to light, new ways of looking at information that had already been available, or newly-discovered flaws in the reasoning behind existing interpretations.
What you're describing is more accurately termed "negationism," so as to not confuse it with the ongoing and perfectly legitimate process of revisionism that is continually occurring (as it should be) within the scholarly community.