In my example, I cited microfractures and weak steel. These are not normal "deteriorate by default" methods of bridge deterioration, and have absolutely nothing to do with proper bridge construction.
They are flaws. Flaws which should never happen, separate from normal environmental degradation.
You may debate the point, but that is irrelevant, for I am referring to abnormal issues with bridges. Flaws in construction. Taking this parallel to humanity, or any evolved species, what "forges" a strong species is constantly being tempered by their environment.
Predation. Disease. Parasites. Even lack of proper nutrition. Environmental adversity, eg exposure to heat, wind, sun, etc. Reproductive errors. Reproduction issues. Etc and so forth. We've eliminated almost all of this, which means that standard methods of evolutionary pressure are almost all removed.
Species do deteriorate by default, if they remain static. Or additionally, if they allow genetic errors (which happens every generation, yes every) to seep into the gene pool without being winnowed back out by the stresses above.
These days, we save babies which are born early. Ones which have a dozen birth defects. Ones which have 100 other issues. Adults (before breeding age) with issues. Note that I am not saying we should not do these things! Only, that there is a price. A long term price.
Now... that being said, I think this is the best part of genetic engineering. It allows us to fix issues like this in the womb, and to get rid of these sorts of errors whilst still helping the current generation live, and have good lives.
But to pretend that evolutionary pressure doesn't exist, is weird. And everything we have which is an enhancement to our survival capabilities, is evolutionarily pressure based.
So back to the start? Those microfractures and weaknesses in steel are not noticeable when the bridge is deployed, as the steel's production is actually the problem. It's years later, with bridge inspections (if done! and they should be!) that these issues are discovered.
But much like global warming, or said steel, you don't want be be performing corrective action. And you can't see it before the issue becomes apparent. People didn't notice the Earth getting warmer when they were burning coal in year 1000 or some such.
We barely see the evidence of global warming now. And it's already too late to arrest some change.
Is that what you'd prefer for humanity? Wait until genetic defects are so rampant that it is "in your face" apparent?