AstroAg17 said:
I googled it and Wikipedia says those diseases are recessive. So if the prevalence of the bad allele is low enough, that person's kid is unlikely to have the disease right?
Yes, the kid will most likely be a carrier although there are a small number of dominant rare genetic disorders. Also there are things like Duchenne muscular dystrophy, which is x-linked. There is going to be a gene therapy cure for this soon (my money is on Pfizer, but I digress) . The cured boy couldn't give it to his son, but his daughter could pass it to his grandson...
I guess a wider point about the current state of the art gene therapies is that delivering a working copy of the gene still leaves the deleterious allele in the gene pool. That's something that gene editing in embryos wouldn't do.