Right now for example the global IQ is decreasing for various factors, but one of them is high-IQ, educated women are less likely to have children. In a few generations, if this trend is not reversed, we will have a collapsing civilisation run by low IQ people who have no idea how to run the systems and technology that they've inherited from us. If you value civilisation, you may wish to reverse this trend. If you don't care then that's a different matter altogether. But for people who value civilisation, high quality traits are things like intelligence, social cohesion, physical health, mental health, co-operativeness, etc.

There's nothing wrong with positive eugenics, ie encouraging high quality people to breed and discouraging dysgenic breeding (eg incest or people with genetic disorders). What's wrong is negative eugenics, ie using state force to sterilise or punish people for it.