You seem to assume reason demands Utilitarianism. I don't agree. People can rationally come to many ethical positions, depending on their value systems. I don't agree with eugenics, and I think I came to that position rationality.
That's circular. Value systems are not rational. People can rationally come to ethical positions but it has to be based on value systems. The value system it's based on isn't objective, so it isn't logical and rational in the sense of meaning of the word that biomerl is applying. Why value human life over other life? That's a value. It can't be logically derived except in relation to other values.People can rationally come to many ethical positions, depending on their value systems.
We're creatures of emotion who use rational decision-making to produce better outcome. One does not exclude the other. One can rationally come to a decision to disregard fear from one's decision-making just as much as one can value fear as a powerful factor in their decisions.
I mean to say that you can use reason and logic to come to the correct conclusion, but in order to do so you need all information necessary to come to a decision. We do not, we didn't have enough knowledge on society to understand that eugenics was bad back when it was popular (Hitler and such). You don't know what we don't know today, so it's important to note where emotions and logic collide and try to sooth the differences.
To clarify, we're using the colloquial definition, of involuntary sterilisation and "shower rooms". I've no objection to people getting together to voluntarily improve the gene pool. As far as classic Ethics goes (Deontology vs Teleology), my general ethical position is an adaptation of Utilitarianism: greatest good for all. That is, each sentient being has infinite value. If it sounds like Deontology—it's not. If two people are tied on a track with a train coming, and you can pull a lever to switch it to a track with one person, ∞ + ∞ > ∞. Incidentally, I also disagree with Deontology, in that I believe inaction is an action. I also believe life is greater than happiness. Call them different levels of infinity, say ℵ₀ and ℵ₁ if you like. So, Strict Utilitarianism says it's ok to kill someone if you provide enough happiness to enough other people, whatever that magic number is. I disagree, because ℵ₁ > n⋅ℵ₀ for any n. But you should still flip that train track, because ℵ₁ + ℵ₁ > ℵ₁ (by my prior declaration; I'm aware that isn't true in cardinal maths [let people be sets, if you like, so it's ordinal maths. People are complicated enough, I think]). Thus, removing the immediate freedom and liberty of one person by sterilising or killing them, in order to theoretically improve the overall happiness of some number of future people, is wrong. ∴ Less traditionally, I really like Rawl's Theory of Justice. In a nutshell, one should act and make laws such that, if there were a birth lottery and you didn't know how you'd be born—black, white, rich, poor—you'd want to live in that world. So, you wouldn't want eugenics because you might end up born disabled or 'genetically inferior'. To address jadedog's comment Value systems may or may not be rational, but my argument is not circular. If no value system is rational, then if one picks an arbitrary value system, and builds a rational ethical position based on it, their ethical framework itself is still rational. Which is important, because a great many people believe in ethical systems which aren't rational, and filled with cognitive dissonance. If you believe no Ethics is rational, which it kind of sounds like, that's a different argument. Which I've countered before, and I'm not terribly interested in making again. Deconstructionism tires me. So we'll have to agree to disagree there, sorry. Greater intelligence. Yes, intelligence is an arbitrary value. But it does seem to make life marginally less nasty, brutish, and short.That's circular. Value systems are not rational.
Why value human life over other life?
If you have read it, what is your opinion on the book, Non-Violence: The History of a Dangerous Idea by Mark Kurlansky? If you haven't read it. You might enjoy it...it is an interesting perspective and is fairly thought provoking. https://www.amazon.com/Nonviolence-History-Dangerous-Library-Chronicles/dp/0812974476 I asked because of your rejection of deontology, which I can support. Sorry for the tangent...and thanks for the new vocabulary word: denotology.