As a transhumanist, I believe that we should aggressively alter our bodies through genetic/technological research and our children (unborn or otherwise, provided we have their consent) to become superhuman and immortal. Eliminate any birth defects which can be defined as anything that would retard your ability to learn, to move accurately and effectively and so on. Anything like learning difficulties such as Dyslexia, Dyspraxia, birth conditions such as Downs Syndrome, the various disorders that lie on the Autistic Spectrum, all that stuff goes out the window.
Though some describe savantism, we should be able to gain abilities like that through alteration of our bodies/genes and so forth. So yes, I believe eugenics is a good idea, so long as it is geared towards improving our physical and mental capabilities (not our thoughts, skin tone etc). The goal that I propose is to give people maximum choice, so they can be whoever they want, as opposed to the more Orwellian stuff like changing our possible thought patterns to ensure that the society is how the state/government or whatever wants it.
Of course, I am not proposing that we exterminate people who have a high chance of producing children with birth defects or whatever. That's just unspeakably terrible - we'd allow them to do whatever they want, either have that tendency to produce kids with whatever defects removed through scientific know-how or leave it in if they want to remain natural. Nobody would force anybody to get a particular edit to their bodies/genes, just like we don't force people to have plastic surgery to make themselves beautiful. One could conceive of a society divided into norms and superfreaks, a bit like the Amish vs the general American public. I think that's the way it should be, though. As long as they don't start killing each-other.
"Selective breeding" i.e. someone picking people to mate with one-another based on particular traits is a bit iffy in my opinion, only though because it involves someone choosing that for someone else. Or indeed, a computer deciding that for someone else. Deciding who would be best for them whether they like it or not etc. I think though if we had the ability to edit our own genes and so on, such as the DNA of our own sperm/eggs, the common conception of selective breeding would no longer apply. People would do all the "selective" stuff in the act of breeding because they'd edit their own sperm/eggs to whatever they wanted at the time. The father and mother would be selective, not the Mating Taskmaster.
So, basically designer babies except without the stuff like changing the thought patterns to suit the parents or changing the skin tone because they don't like whites/blacks and so on, or changing the gender because you want a girl/boy. You'd choose what "powers" or abilities you wanted to give your child, most likely based on your financial/cultural situation. Unless governments take this over, which is a matter of some consideration because there could be all sorts of ugly things that come about as a result of governments gaining such powers. Hopefully technology would exist by that point to allow the child to get the abilities they want and don't have, provided they meet the criteria.