A noted anti-evolutionist moonbat Casey Luskin makes a fuss about atheist anti-creationist Larry Darby, who also happens to be a Holocaust denier.
He also complains that some "Darwinists" have compared ID creationism to Holocaust denial. Well, boo-hoo! If it walks like a duck and quacks like a duck...
Orac urges to be cautious about such analogies. I respectfully disagree.
It is true that every time evolution denial methodology is compared to Holocaust denial methodology, both denier groups tend to be offended (that is, unless someone is both an evolution denier and a Holocaust denier).
That does not detract from the validity of the comparison. Moreover, the comparison is almost perfect - moon landing denial does not come close. Here are several most important similarities - as I see them.
1) No credible alternative (scientific/historical) theory.
Evolution deniers cannot account for existing evidence for evolution. At best they don't offer any alternative, at worst they appeal to some sort of miraculous Designer and implausible ad hoc arguments.
Holocaust deniers cannot account for the missing Jews. Stupid deniers simply say that none are missing, without explaining where millions of Jews deported to specific places, and not found there after the war, went. Smart deniers are silent on the issue.
2) "We don't deny micro...!" tactic.
With some exceptions, evolution deniers love to repeat that they accept microevolution, but not macroevolution.
Not quite in the same terms, but Holocaust deniers use the same rhetoric. You can often read that such and such does not deny the [micro-]Holocaust. Sure, bad things happened to, maybe, a million or so Jews - typhus, you know. But there were no gas chambers and no systematic extermination [i.e., no macro-Holocaust].
3) "No empirical evidence" whine.
Evolution deniers often claim that there is no empirical evidence for evolution, e.g. speciation, or transitional fossils.
Holocaust deniers claim that there are no credible documents proving the Holocaust, or that there are no mass graves.
4) "What do they have to hide?/Persecution!" demagoguery.
Evolution deniers sometimes claim to be persecuted, and charge that "Darwinists" are out to stifle the "debate", as if they have something to hide.
Holocaust deniers at least have grounds for claiming that they're persecuted (in several countries), and they also argue that this persecution has something to do with stifling the "debate", and hiding something.
5) Search for irrelevant "icons".
Evolution deniers are fond of complaining about the so-called "icons of evolution" (gill slits, Haeckel's embryos, peppered moths), which complaints, even if true, would not establish the falsifty of evolution. This has nothing to do with truth-seeking, these "icons" are used for purely rhetorical purposes.
In exactly the same fashion Holocaust deniers try to "debunk" the Holocaust by bringing up minor and irrelevant details, such as human soap and lampshades, Dachau gas chamber, or Auschwitz plaque with 4,000,000 victims.
6) "Show me, step by step!"
Evolution deniers (especially ID creationists) are fond of demanding to describe, step by step, evolutionary pathways leading to the biological systems of their choice (usually, the so-called "irreducibly complex" systems). When plausible, though maybe not "step-by-step", pathways are presented, they're routinely dismissed. If no pathway is presented, evolution deniers claim victory.
Many Holocaust deniers are fond of Robert Faurisson's "Show me or draw me a gas chamber!" slogan. Of course, when the drawing is presented, this changes exactly nothing.
7) "Exception disproves the rule" rule.
A widespread tactic. E.g., evolution deniers argue [PDF] that variant genetic codes prove that the genetic code itself is not universal, and that these codes actually present a challenge to common descent.
Similarly, Holocaust deniers argue that if Anne Frank was deported to Auschwitz, but wasn't gassed there, and rather died of typhus in Bergen Belsen, then the "story" about murderous selections in Auschwitz is not true (regardless of specific circumstances which may have caused the exception).
Addendum: 8) And, of course, both Holocaust and evolution deniers claim that, respectively, the Holocaust and evolution are religions, and blame all sorts of real and alleged social ills on them. Holocaust deniers usually blame the "Holocaust industry" for persecution of Palestinians and post-war liberalism. Evolution deniers usually associate evolution with moral decay, atheism and liberalism. Holocaust deniers sometimes produce an alleged quote by Claude Lanzmann that "Auschwitz is the refutation of Christ" to prove that the "Holohoax" is an attack on Christianity. In the same vein evolution deniers like to quote Dawkins' attacks on Christianity.
There are more similarities, but that's already enough to show the almost identical modus operandi of both denial groups.
Now, on a purely rational level it is absolutely irrelevant that Holocaust denial is extremely offensive. If it were a legitimate critique, it should have been taught without any regard for "offensiveness". If it is factual, it should be taught.
Therefore the question about why we can teach evolution denial ("the controversy") but not Holocaust denial (also "the controversy") is absolutely legitimate. Those evolution deniers who would try to change the topic and complain about unfair comparison to "the Nazis" are demagogues, pure and simple.