I have some pretty strong feelings about eugenics (it's a good and necessary practice), but I find it very, VERY difficult to talk about it with anyone since I'm instantly labeled a Nazi for supporting it. I'm hoping the folks on Think Atheist will be more inclined to intellectual discussion than name-calling and dismissal.
The start off, some disclaimers: genocide is wrong; taking human rights away from people of a race/religion/hairstyle you don't like is wrong; concentration camps are wrong; violence in wrong.
There. Now to the actual discussion.
When I talk about eugenics, I'm talking about the practice of systematically removing debilitating genetic traits and defects from a population by means of regulating the reproduction of its citizens. Do you have Schizophrenia? Did you know that this ailment is genetic and very easy to pass on to you children? Please, do not punish an innocent child with this problem. Are you genetically healthy, intelligent, and talented? Do you have special immunities that make you less likely to get sick? By all means, spread these traits to future generations, either by having children yourself or donating to a sperm or egg bank. Do you want children but should not carry your genetic problems onto them? Adopt. Adoption will always be available no matter what the society (just because someone has good genetic material does NOT mean they would make a good parent). Do you say that adoption is not the same? Then I suppose you care more about satisfying your selfish desires than the well being of a child.
Eugenics is, at its base, very simple - think about the future first.
I'm leaving this post now for what I'm hoping will be thoughtful and anti-inflammatory discussion.
In a liberal society, the state may only interfere with liberty when it has an overriding duty. On balance, the opinion of some, even most, that less than optimal genetics ought to be avoided does not amount to an overriding duty to act. (Consider for example freedom of speech ... distasteful opinions can't be censored, but speech that threatens public safety can.) Therefore, whatever sort of "genetic hygiene" people wish to pursue has to be voluntary, unless you want to live in a fascist state.
As medical science advances, more and more people are already practicing voluntary eugenics, and even going the other way by trying to rig the genetic game to produce superbabies. I say more power to them, as long as they are making free choices for their own reasons.
"Therefore, whatever sort of "genetic hygiene" people wish to pursue has to be voluntary, unless you want to live in a fascist state."
That's an argument which only works if you assume that today's standards of what's acceptable and not is similar to what tomorrows standards are. You can pretty much put anything in those quotation marks, it's the Fox news way of rejecting new thought.
(To paraphrase you, does this sound like something you could hear Bill O'reilly say: If "homosexuals" want to marry, then can go to the Netherlands (read: fascist/socialist/morally bankrupt state)."
On the preventing people from breeding part. There's already an "evil" plan there. Give every people a strong government, a good education, and preferably some money, and we won't even have replacement rates for a while. Essentially bribing them to not have children.
Then when people get tired of chasing money, they'll also want about what they can afford, probabliy around a couple of children to raise, thus ensuring a stable population which will probably fluctuate in response to what the macroenvironment has to offer.
I think that it's an almost meaningless arguement, because transhumanism makes eugenics obsolete. Some may say that most of the accomplishments of eugenics that could theoretically be replaced by transhumanism don't exist yet, however while two people can experiment with selective breeding instantly, dramatic results are going to take much more time(generations) than transhumanist technologies would to develop.
Ignoring all ethical and moral aspects, even from a completely utilitarian perspective, the amount of money that it would take to enforce involuntary selective breeding on a widespread scale is probably much more expensive than developing a cost effective embryo screening service. A company called the fertility institute announced that they were going to start development on a business model for that but, they quit because of a pretty dramatic negative reaction from the general public. Furthermore, embryo screening would do way more than eugenics could accomplish.