PZ Myers on the idea that 'Dawinism' (whatever that is supposed to mean) leads to eugenics:
It is nicely put, but probably destined to be misunderstood by several varieties of idiot.
The point is that before Darwin, sensible people (such as farmers and other plant and animal breeders) knew about artificial selection. You can eradicate a trait by breeding it out, if you really want to. In other words, eugenics certainly predates Darwin, who pointed out that evolution could occur naturally, without any decisions, based on what does and doesn't happen to survive and reproduce.
Eugenics is entirely artificial selection, not natural selection. The confusion comes from a misunderstanding of the term 'survival of the fittest'. Hopefully, I don't need to spell this out.
Oh go on then:
Darwin: Organisms compete, albeit not on purpose. They reproduce or not based on how they interact with their environment. The result is differential changes in frequency of genes in a gene pool and therefore gradual changes in phenotypes.
Eugenics: Let's pick and choose which organisms should survive based on an arbitrary distinction. The result is differential changes in frequency of genes in a gene pool and therefore gradual changes in phenotypes.
The result is the same kind of thing, but the distinction is outrageously obvious, which is probably why it takes someone like PZ to point it out. To people who understand evolution it is like pointing out that what goes up tends to come back down.