I have no doubt that it's tangential to your point, as you supplied substantive arguments against eugenics in addition to the nonsense argument I took exception to; but no, I was not objecting to a common argument that I don't like. I was objecting to your argument. And since your argument plays the same word-games on "fittest", Dawkins' comments on the common one apply every bit as much to yours.
Yes, you did specifically discuss the Theory of Evolution, when you wrote "The Theory of Evolution says that those who reproduce are the fittest.". Then you added that this "is the definition of fitness". That would make the former statement mean "The Theory of Evolution defines 'fitness' to be 'those who reproduce'.". But that is not the case. The Theory of Evolution does not say that. The Theory of Evolution is not a dictionary. It is not in the business of defining words.
Furthermore, there's no causality in a word definition. So eugenics could hardly be based on a reversal of it even if eugenics were founded on the idea that those who are the fittest should reproduce, which it isn't. (It's based on the idea that those who are genetically the
best should reproduce. In the "Idiocracy" scenario eugenics supporters typically propose to avert, the problem is not that
the unfit are reproducing; the problem is that
stupidity has become a higher fitness character than
intelligence.)
And finally, "those who reproduce" is not
the definition of fitness; it's
a definition. Dawkins exhibits five different definitions used in biology. So no, even if eugenicists thought that those who are the fittest should reproduce, that would hardly leave them in need of a new definition. They could easily pick one of the other old ones.
The rest of your criticism of eugenics is no concern of mine. Tell it to Abe.
That the equally foolish idea underlying libertarianism - the idea that all choices are purely private - is needed to prop this claim up does nothing to improve the standard of the argument. Eugenics is a stupid idea; and that it requires the stupid idea of libertarianism to support it does not render it less stupid; quite the reverse.
That libertarianism is a stupid idea underlain by a foolish idea I will not dispute; but your hypothesis that the underlying idea is that all choices are purely private is itself quite foolish. Libertarians recognize all sorts of choices as non-private; and their widely varying philosophical justifications for libertarianism are quite consistent on that point. You seem to be making a habit of arguing against lame caricatures of the ideologies you disapprove of.