"Blood" euphemisms are commonly used by antisemites and racists of all types. Hitler made many reference to "German blood, "Jewish blood," "our blood," and so on, essentially as shorthand meaning ethnicities. The KKK repeatedly emphasizes the importance of "blood purity" to promote its ideology. Which is why Trump's recent claim that immigrants are “poisoning the -blood- of our country” got so many people riled up--it's an obvious dogwhistle, using the preferred terminology of some very, very bad people.
Thank you for shining light on these examples for me. I've been studying quite a bit of history, esoteric spirituality and the occult sciences over the past few years and have fallen into the habit of using this term when talking about lineages of influential people and their families.
I definitely did not mean to sound like I was into eugenics or racial purity - I think these concepts are grotesque and as you said, people that focus on them or use them to excuse atrocities are indeed, very bad people. Thank you for giving me the benefit of doubt and highlighting why my choice of language is problematic.