"do you view Gregor Mendel's studies to be in the category of "amoral science" with a "direct line" to Hitler and the Holocaust?"
The "rediscovery" of Gregor Mendel in the very early 1900's certainly gave a popular boost to Galton and eugenics, but it cannot be said to have influenced Galton in penning "Hereditary Genius," as he was unaware of Mendel's work at the time. Did Mendel's study of dominant and recessive traits in peas have any influence upon Nazi eugenics programs directed at human beings? Only to the degree that it added a further, scientific sheen of justification for eliminating people deemed undesireable, whether by the Eugenics League or by the Nazis in Germany. Mendel did not, however, delve into the relative worth of this or that "race" to society. Galton did.
That "only" seems a little disingenuous. Mendel's work didn't just provide an "added scientific sheen," it provided experimental and foundational justification for the core concepts of eugenics. Nazi geneticists implemented entire programs of "genetic cleansing" based upon notions that derive directly from Mendel.
Mendel did not, however, delve into the relative worth of this or that "race" to society. Galton did.
Surely you're not suggesting that Galton, or Darwin, invented racism.
And I trust that you aren't suggesting that all instances of ethnic cleansing and genocide post-Darwin have a "direct line" to him (or Galton, or Mendel). Somehow, I doubt you're going to find any connection between the ideas of Darwin and, for example, the genocides in Darfur, Bosnia, Cambodia, or Rwanda.
The Tutsi and the Hutu engaged in wholesale slaughter for the same, rather old-fashioned reason that Hitler targeted Jews -- ethnic and religious hatred and scapegoating -- and that "idea" has been around for a pretty long time.