The core component of fascism is authoritarianism with totalitarian goals. Many nationalist movements throughout history have not been fascist in nature, and many non-fascists have embraced nationalist values without becoming fascists.
Also, claiming that a rise of fascism is inevitable under social liberalism is speculation at best.
In addition to what @LwL said - It has to do with how testing is done, and that some diseases can’t really be tested for. It is quite expensive, and is generally done on small samples from lots of people mixed together. If it is positive they split the batch and test again (look up binary search).
The lower the incidence rate of diseases, the larger batches can be done. Ditching certain denographics with significantly higher risks for certain diseases can make testing orders of magnitudes cheaper and faster. (Other groups, at least where I live, include people who recently changed partner, recently went abroad, have ever gotten a blood transfusion, have gone through a recent surgery, have recently been sick, etc. etc.)