If you read the entire article, the unstated fart in the elevator is that Democrats were the ones to jump on eugenics as a "scientific" justification for segregation, miscegenation, colored drinking fountains and bathrooms. You can delude yourself however you want, but the fact remains that eugenics was adopted by both parties.
Eugenic sterilization was imposed throughout the country. The Nazis modeled many of their laws after California and California was pretty solidly Republican until the 1970s. Oliver Wendell Holmes, Jr. was a Republican.
Republican and Conservative are two different animals, if you haven't noticed. Republicans will jump on any bandwagon, suck any, ummh, toe, if they think it would make them popular with the lumpen proles. We have to tolerate Republican "leaders" because we're too civil to do to them as they deserve.
When Jefferson spoke of watering trees, he didn't specify party membership.