By far, one of the most egregious claims made by creationists is that somehow the theory of evolution is responsible for the Holocaust.
Now for the purposes of this discussion, I will set aside two undeniable facts:
1) the claim is pure, unadulterated, bullshit.
2) it would have no effect whatsoever if Hitler had quoted Darwin in every third sentence of Mein Kampf. One very evil person's opinions do not, in themselves, constitute an argument against any given position.
I'm going to set both of these aside for the moment and ask something a little more fundamental: if, indeed, Hitler were motivated purely by Darwin's theory of evolution, does the Holocaust even make sense?
Of course, one could posit that Hitler's approach is based upon a misunderstanding of the theory of evolution, but that can hardly be blamed on the theory. So, in the interest of full disclosure, in this little thought-experiment, I will make one assumption which I'm sure will be considered reasonable: Hitler actually understood the theory of evolution beyond the typical creationist straw-man versions of it. In other words, he understood what the theory of evolution actually says, rather than what creationists say it says.
So, if one was a dictator, motivated purely by an understanding of evolution, what would one do? In short, how, as a maniacal dictator, would one go about maximizing one's evolutionary potential? Well, in order to do that, one needs to first look at nature and ask what the most successful organism on the planet is, and see if there is any way we can mimic its behaviour.
Creationists are fond of claiming that human beings are the pinnacle of evolution. We're the most successful species on the planet, according to their version of evolution. This is, by any standard pertinent to what evolution actually says, false.
By any standard pertinent to evolution, the lowly e. coli bacteria is among the most successful organisms on the planet. Bacteria in general (and yes, I know, I'm talking about a whole kingdom here, rather than a species) are now, and always have been, the dominant organisms on this planet. They kick the asses of the entire animal kingdom in terms of reproductive rate, adaptability, and number of individuals, biomass, and environments exploited. By these standards, the only standards pertinent to evolution, all of the eukaryotic branches of the tree of life combined (that includes plants, animals, sponges, anything multicellular, and absolutely every living thing you can possibly see without a microscope) cannot even come close to matching the success of the e. coli species of bacteria alone.
A dictator, familiar with what the theory of evolution actually says would know this. Such a dictator would also know that it is beyond our technical capabilities to cause the human race to revert to the prokaryotic stage.
So, given this limitation, what is a dictator to do?
Well, short of reducing the human generational time to a matter of hours, rather than years (also beyond our capabilities), the next best option would be to increase the level of biological diversity as high as you possibly can. Actually, the most sure-fire way of guaranteeing a population's extinction would be to reduce the gene pool of your populus. Since extinct populations generally don't evolve any further, it seems unlikely that a dictator familiar with what the theory of evolution actually says would take this course of action. Put simply, if Hitler were actually motivated by the theory of evolution, the absolute last thing he would ever, ever want to do is create a "master race." In fact, were he motivated by what the theory of evolution actually says, he would know a "master race" of any kind; whether black, white, fuchsia, mauve or green; should be avoided at all costs.
There are any number of ways in which the genetic diversity of a population can be maximized, and while none of them are particularly palatable options, they're certainly not what Hitler did.
First off, some form of breeding program is a must. Not to breed out specific characteristics, mind you, the way that you do with dogs. The objective here would be to create the human equivalent of a mutt. Women will have to be required to produce offspring with different men of different ethnic backgrounds. This breeding program will have to go on for generations. After 6-10 generations or so (when we're breeding mice, we generally go with 6), it will be virtually impossible to tell that you have "races" at all in your population.
Next, from any country you conquer, the population which survives the conquering process will have to be included in the above-described breeding program. For example, it would be to your benefit to make sure that the gene for sickle-cell anemia exists somewhere in your population, as this has as a benefit a near-immunity to malaria. This gene exists almost exclusively in African populations. There's also a family in Greece which has a mutation which allows them to more efficiently process low-density lipoproteins. As a consequence, they have no family history of heart attacks. In tibet, a population has a gene which allows them to survive better at higher altitudes. Since none of these exist inherently in Germany, and very few exist in the caucasian races, limiting your genetic diversity to one race is, frankly, stupid.
Like I said, this will likely have to carry on for many generations, so you'll also probably have to do something about that whole "mortality" thing.
Now, we can argue about the ethics of this approach, and I agree, I'm not terribly keen on it myself. However, I think that there's one thing we can all agree on:
It's not what Hitler did.