If you want to really extend the natural selection argument -- you could very soundly argue that modern medicine is making us as a species significantly weaker.

We now can do wonderful things like saving newborn babies with perforated diaphragms or under developed lungs at birth... In the microcosm of that single family it's a huge blessing.

But we're perpetuating those genetic flaws throughout society... Is that good?

Eugenics anyone?

(FWIW I am not at all on one side or the other here, just think it's a fascinating unintended consequence of modern medicine saving so many young people from genetically inherited defects/diseases)