If we can create stronger horses through selective mating, why do you believe that would not carry over to intelligence if applied to humans? Why would it not be worth having stronger, healther, and more intelligent humans?
Maybe you do a good job, but this sort of power will inevitably become corrupted by a failed art student sooner or later.
I don't mean that as an insult. I mean it as an inevitability.
Everyone who promotes eugenics always imagines themselves as being the superior one.
To answer your question : If I were born with a horrific disease that has a significant chance to pass that down to the next generation, it would be my responsibility to not pass that down to the next generation. I would understand.
There are always superior people and inferior people depending on a multitude of variables : time, genetics, intelligence, environment, training, etc. Ignoring genetics as an essential pillar of this is irresponsible.