> Also humanity and evolution has a coping mechanism called natural selection.
So the phrase "Survival of the Fittest" refers in the abstract to the idea that, given fitness function F, members of a species who pass fitness function F will out-survive members who fail function F and then reproduce in higher numbers. But natural selection itself does not define any fitness functions, and makes no mention of a "universal fitness quality" that can be used to judge the fitness of an individual.
The fitness functions that nature comes up with are pretty arbitrary, and don't necessarily align with cultural ideas about merit, fitness or attractiveness. A disease that weakens bones could kill more tall people than short people, a disorder that exploits muscle tissue might affect people who work out more, and a respiratory disease that spreads through the air could take down more sociable people while allowing introverts who stay inside to survive.
The point of modern medicine is that we recognize these many of these fitness functions have no meaning beyond the immediate danger they present. And we can use technology to say "that fitness function is dumb" and remove it from the equation. In doing so, we aren't "unlearning a lesson nature wanted us to learn", we're protecting ourselves from the meaningless and arbitrary rocks that nature occasionally throws at us, and as a result we are increasing human lifespan and quality of life. (And yes, you can quibble about stretching out the suffering of people with terminal cancer, but the millions of children who don't pointlessly die of infant diarrhea each year would probably push back a bit)