Primarily, Doctors' efforts are often diluted by the masses of injured people with the flu and other simple pains that ARE annoying but ultimately NOT life-threatening in the majority of cases. If humans were essentially better at healing themselves or not being hurt in the first place, More serious pains and illness only would go to doctors in the majority of cases and the very minor things would never happen or heal themselves more efficiently, Instead of the chronically backed-up hospital system currently in place in most developed countries.
I believe we should only do this in extreme cases. We can detect severe defects very early with upcoming technological advances such as downs and even worse horrible genetic defects that let a child not go past just a few years in age. In my opinion if we can prematurely detect these genes and terminate the pregnancy, OR adjust the genetic make-up for this we should. However we should forbid it for non life threatening things such as knee related injuries, We will get into a culture of designer babies where parents can design everything about their children, Eye colour, Length everything. And people will strive to 'create' the 'best' children. We also can't really realistically locate every single gene for everything yet and pass it onto every single cell. Also I would also consider conditions such as Downs Syndrome under 'life threatening' not because it can be fatal but because it very significantly threatens a childs quality of life.
Michal Phelps has a genetic defect. He was told to swim to improve his condition and he became a gold medal winner.
Some genetic conditions can be treated and medicine is improving. There some that are severe but we can learn and treat them.
Genetic editing is something that will be abused and ruin the human race.
So in star trek they made super humans in the past. The superhumans became rulers and caused harm on earth so they were sealed away. What is the chance of a superhuman deciding that normal humans should be wiped out.
Second the class disparity will be even higher. How can some normal joe compete with an enhanced human in a job. You will force people to have enhanced children or doom them to be "inferior"
Sports will no longer be the same. Racing and other jobs will change.
And finally the DANGERS. Genes can be coded backwards. You do not know the consequences of changing or adding a gene. You could be making the population at risk for becoming sterile in the future or having a new weakness.
Do not tamper with genes. You will mess up the human race. And you will open the can of worms of owing people and genes