"But saying "Nazis might use it against us" is not a downside, that's just insane."
At this point you aren't arguing, you are just engaging in abusive name calling.
Whether its racist national socialists or well intended eugenicists paving the road to hell, it is ENTIRELY possible. The entire first half of the twentieth century was full of eugenicists in the U.S., Britain and Germany trying to select out genetic flaws in humans, often using force. California and the Rockefeller foundation pioneered forced sterilization of people with genetic defects. The only reason eugenics died out was because the Germans gave it such a bad name.
Now that we have tools to actually study genes in detail, to manipulate them and really do eugenics its nearly inevitable its going to return in some form.
There is a hard right neo nazi regime in Hungary already, the hard right came in third in the last French election, and an antisemitic neo Nazi party gained seats in the last Greek election. With Europe on the verge of a major economic collapse its entirely plausible there will be more neonazis in power in Europe in the near future. Economic collapses breed national socialism and persucution of ethnic minorities who are scapegoated for the collapse.
P.S. The benefits of vaccines probably out weigh the risks but they have serious down sides too which just shows how biased you are. Some people have violent and dangerous reactions to some vaccines. There is a Federal agency that does nothing but compensate people for adverse reactions to vaccines, its called the National Vaccine Injury Compensation Program
Polio vaccines were made with monkey tissue and some batches were contaminated with a dangerous simian virus that was a carcinogen, some people have also been infected with the disease by the oral vaccine. The mercury in Thimerisol was never proved safe which is why it was removed, but large numbers of people were injected with it. For diseases like chicken pox getting the disease and building natural immunity may be superior to vaccine immunity. People with immune system disorders can actually contract some diseases from vaccines.
