Even in humans, we occasionally exercise “selective breeding,” like when potential carriers of Tay-Sachs (an absolutely horrific disease which mostly affects people with Ashkenazi heritage, and whose sufferers have an expected lifespan of a few years of horrible pain) and their partners choose to be tested before deciding whether or not to have children. Even with the context that mostly Jewish peoples’ genes are tested to see if they should have children, it’s not considered eugenics, because it’s an entirely voluntary process. Even if two people are both carriers, they aren’t prevented from having children, nor is their genetic predisposition shared with anyone.

Incest laws are essentially a way to restrict peoples’ choice of partner to ensure genetic vigor (that’s why they’re different for relationships which could and could not produce children). Even that’s not generally considered a form of eugenics, because it applies to people, without regard to their specific genes.