Civilized discourse does not require both sides recognize the validity of any argument of the opposing side.
Yes, we agree..the inherent problem with eugenics is that ultimely, it's about breeding to a standard, and culling all those who do not meet the standard.
It's one thing to choose your own mate with that in mind..it's another to force that standard upon others. And that is exactly what forced sterilization is. Forcing a eugenic standard upon people whether they agree or not, and it has never in the history of mankind been anything but a deplorable and disgusting mess when any group has attempted to do that, in any degree.
You're right. Civilized discourse does not require that. However, to assume that all who advocate some form of eugenics have nefarious intentions is not exactly conducive to civil discourse either, and that is what you are suggesting. Birth control as a means to discourage unwanted pregnancies and decrease the number of babies born to unfit parents is something I advocate, and which eugenicists advocate for the same reason. While that doesn't make me a eugenicist, nor mean that I advocate state enforcement of forced sterilization, it does mean that I share something with eugenicists, and I must concede that eugenicists have at least some motive for good. If I simply dismiss eugenics and those that hold some belief in the concept as evil or ignoble, or assume only the worst of intentions, there is nothing to be gained. There is nothing civil in assuming that somebody who advocates some form of eugenics is a Nazi.
Eugenics in an of itself IS nefarious. You can make excuses all you like about how civilized the proponents of it are, and how "noble" the concept is, but you are wrong, of course. Eugenics has ALWAYS had proponents declaring that the concept is sound. But the truth of the matter is, the concept ISN'T sound, not for humans. The concept is appalling, and applying negative eugenics to others is always a violation of human rights. You cannot recognize that human rights exist and should be defended, and at the same time parse words and support, but not support, negative eugenics.
The most oppressive tyrannical despots have depended upon the *civilized* and *scientific* community to support them in their application of negative eugenics, and they still do. Perhaps you don't have nefarious motives...but I promise you, the people who will benefit from the abuse of this *civilized* and *noble* method of culling despised populations, do.