In and of itself, eugenics is a good thing. I would love to see it advanced. The research could lead to the cures for cancer, diabetes, heart disease, possibly even make our entire race stronger and smarter. The possibilities are endless.
The possibilities are almost nonexistent, actually. In order to alter a population significantly without it backfiring horribly (see dog breeding for a good example of backfiring), you need extremely advanced genetics to determine who can safely breed with whom, at which point it's a lot easier and safer both technically and ethically to just use gene therapy.
This is, of course, all ignoring the social framework needed for eugenics. After all, simply telling people not to breed is not going to be effective unless somehow enforced. Whether that force comes from outright violence or extortion ("no welfare for you unless you let us mutilate you"), it carries a horrible price even for those who are not themselves victimized.
So no, eugenics is not a good thing. It's inherently evil due to harming people and the entire society for empty promises. It would likely still be evil even if it could actually fulfil those promises, but it can't. And talking of it as "in and of itself" to avoid thinking of all it implies is downright dishonest.