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.
"Surely you're not suggesting that Galton, or Darwin, invented racism."
No, but they provided the scientific rationale for it, in the instance of Nazi genocide.