Selective breeding or selective sterilization fail under Fairness, Rights, and probably Common Good. Maybe you’d get a pass with embryonic screening, but you’re fall afoul of other considerations there. Preselection of specific eggs and sperm before fertilization might clear most of those hurdles. So unless you get everyone to measure by only one ethical measurement, you’ve lost right out of the gate.
Genetic engineering is probably acceptable to most under all five. You’d probably still have ethical arguments. GE has ethical arguments raised against it in general, but let’s not go into the baby and bathwater arguments here. Editing genes in a fertilized egg or a blastomere has different ethical implications than doing gene editing in a fully born person. It’s different for a patient who can consent and for a child, too.
Cystic fibrosis usually leaves men mechanically sterile, although not carriers and men with CF can still have children through medical/surgical interventions. Its complications are ever more treatable. There are over 2500 known mutations of this gene, accounting for about 30 different disorders including CF. Which mutations would you screen for? Who among the population would you screen - known carriers? People with any CF in their extended family? Everyone?
As to what specific gene or sets of gene in mind to alter, that depends on what you define as "bad things" and what is possible.
From a rapid google search, Cystic Fibrosis seems like a candidate.