The Nazis were eugenicists and Malthusians (see Mein Kampf, chapter 4). They wanted to murder "the inferior" because they were convinced there wasn't enough food to go around. The Malthusianism told them that millions had to die; the eugenics told them who the victims ought to be.
Strangely, though, the Nazis' crimes discredited only eugenics, not Malthus. After the Holocaust, you'd think that anyone muttering, "There are too many people running around," would be an instant pariah. But that's not how things worked out.
This is especially strange because there's nothing intrinsically misanthropic about eugenics. As I've explained before, eugenics plus the Law of Comparative Advantage leads to trade, not barbarity:
Suppose we have an isolated society in which everyone is a genius.
Let's call them the Brains. Who takes out the garbage? A Brain,
obviously. Who does the farming? Again, Brains.
Now what happens if the geniuses come into contact with a society
where everyone is of average intelligence at best? Let's call them the
Brawns. If the Brains allow the Brawns to join their society, the
average genetic quality of the Brains' society plummets. But everyone is better off as a result!
Now the Brains can specialize in jobs that require high intelligence,
and the Brawns can take over the menial labor. Total production goes
Malthusianism, in contrast, is intrinsically misanthropic. By hook or by crook, population has to go down. Sure, they'd prefer voluntary sub-replacement fertility. But if that's not in the cards, the next steps are government pressure to discourage fertility, then caps on family size, followed by forced sterilization, mandatory abortion, and finally mass murder.
An hysterical straw man? Hardly. Malthusianism was Hitler's official argument for his greatest crimes. Germany's problem, in Hitler's own words:
The annual increase of population in Germany amounts to almost 900,000
souls. The difficulties of providing for this army of new citizens must
grow from year to year and must finally lead to a catastrophe, unless
ways and means are found which will forestall the danger of misery and
After considering all the viable solutions within a Malthusian framework, Hitler picks his favorite: Seizing more land in Europe.
Of course people will not voluntarily make that accommodation. At this
point the right of self-preservation comes into effect. And when
attempts to settle the difficulty in an amicable way are rejected the
clenched hand must take by force that which was refused to the open hand
of friendship. If in the past our ancestors had based their political
decisions on similar pacifist nonsense as our present generation does,
we should not possess more than one-third of the national territory that
we possess to-day and probably there would be no German nation to worry
about its future in Europe.
As I sum up:
When someone says "There are too
many Jews," we suspect that he wants to kill Jews. Similarly, it turns
out that at the root of Hitler's propensity to kill people was his belief that there are too many people.
My claim is not that, "Malthusianism is false because Hitler believed it." Hitler presumably believed that the sky is blue. My claim, rather, is that Malthusianism is a more dangerous doctrine than eugenics. If the whiff of eugenics leads you to say, "We should be very careful here, because these ideas can easily lead to terrible things," the whiff of Malthusianism should inspire even greater trepidation.