> I mean, if we wanted every human on Earth to be over 6' tall, we could just cull the short ones (or stop them from reproducing), and this is scientifically valid, but, of course, evil.

What's scientifically valid about that? What part of the scientific process is being utilized? What hypothesis is being tested?

If you're implying that people would start to be taller because we are culling short people, then you're talking about "artificial selection", not "eugenics". People who believe that there are groups of humans that are inferior or superior based on genetic differences would love for you to conflate the two concepts because that gets them closer to their political goals that have historically resulted in unimaginable human suffering.