The marketplace of ideas means you don't get to dictate what others find relevant.
For some, this means that they don't want to be professionally or socially associated with someone who thinks some ethnic groups make genetically good slaves. People can vigorously discuss whether his writings crossed lines of acceptable behavior.
However, you're also free to discuss the technical details as much as you want! If that's what's relevant to you, that's perfectly acceptable as well, and it doesn't require you to defend his other writings.
For some, this means that they don't want to be professionally or socially associated with someone who thinks some ethnic groups make genetically good slaves. People can vigorously discuss whether his writings crossed lines of acceptable behavior.
However, you're also free to discuss the technical details as much as you want! If that's what's relevant to you, that's perfectly acceptable as well, and it doesn't require you to defend his other writings.