Broad-brushing Sanger as some kind of eugenics monster is intellectually dishonest. She was a proponent of negative eugenics. From Wikipedia:

In contrast with eugenicist William Robinson, who advocated euthanasia for the unfit,[note 7] Sanger wrote, "we [do not] believe that the community could or should send to the lethal chamber the defective progeny resulting from irresponsible and unintelligent breeding."[108] Similarly, Sanger denounced the aggressive and lethal Nazi eugenics program.[103] In addition, Sanger believed the responsibility for birth control should remain in the hands of able-minded individual parents rather than the state, and that self-determining motherhood was the only unshakable foundation for racial betterment.[109][105]

I think her advocacy for self-determining motherhood is why conservatives hate her.