"Any gene that associates with poor quality of life or diminished lifespan?" So there are about 300+ genes in Gene age that are associated with longevity. Many that are a simple SNP that in some cases confer an extra 5 years of lifespan - would this be ok to fix?
I think "good medicine" supplies the criteria for any example someone could offer. No medical procedure can guarantee a certain lifespan, but many can alleviate suffering and improve quality of life, so the criteria should be focused on that. Take diabetes - definitely shortens life, definitely causes misery, and I can't think of any positive thing that the 6 (I think that's a figure I've heard) alleles involved would be worth preserving for in the human genome. Unless we think it's great to have people gain a lot of weight before a famine. How many people would step forward and say, "You know, the way I gain weight so easily should definitely be kept a part of our species' genetic legacy, and I would like to volunteer to carry on that great tradition! No gene snips for me!"
And, as the article notes, if the patient really is concerned about not tampering with their "legacy," they can still get the somatic cell only therapy. Also, an option, as noted, when the gene function is not totally clearcut. In a world reverting to malarial jungle, some might want the advantage of heterozygous sickle cell gene for future generations.