To be fair the Nazis sucked at eugenics. When you have 5 foot nothing, piggy eyed, dark haired Himmler heading up your extermination camps by shipping off blonde haired blue eyed Jews and Slavs, you aren't exactly promoting your aryan ideal.  But yeah eugenics on a small scale is just don't reproduce with bad genetics, and on s large scale is basically sitting down and saying you know what some of these genetic disorders are bullshit, let's just kill everyone who has it and be done with it; AIDS sucks, let's eradicate it by culling all carriers, etc.