OK, I hope my question doesn’t get misunderstood, I can see how that could happen.
Just a product of overthinking.
Idea is that we can live fairly easily even with some diseases/disorders which could be-life threatening. Many of these are hereditary.
Since modern medicine increases our survival capabilities, the “weaker” individuals can also survive and have offsprings that could potentially inherit these weaknesses, and as this continues it could perhaps leave nearly all people suffering from such conditions further into future.
Does that sound like a realistic scenario? (Assuming we don’t destroy ourselves along with the environment first…)
The more varied the sample of individuals you can afford to keep alive in your population, the more chances you have that a subset of them will be able to withstand random changes in the fitness function. If the environment changes abruptly, you will have a hard time adapting as a species if you only ever supported people “within the norm”. What happens in those cases is called extinction.