As a starter, I'm extremely sceptical of modifying the genome of embryos (as I hope was clear from my comment). Like you said, there's plenty of defects that can have advantageous sides in addition to the negative sides. My point is that the only way this could even conceivably be ethical to do, is if it was used to remove diseases.

I believe there's already a procedure they do to remove a disease carried in the mother's mitochondria. I heard about a rare disease from my dentist the other day that causes people to never grow any teeth. I'm saying that if this is done, then the only ethical thing to do is use it for population-wide removal of severe diseases with no known positive sides, and even that can be dubious (as you point out).

aren’t bound to Evolutionary advantage to survive.

That's not how evolution works though. Evolution is a process that works a the gene-level. A gene that makes its carrier more likely to reproduce and keep its offspring alive will over time propagate and replace genes that are less likely to do so. This is a simple game of statistics that works regardless of whether the organism that carries the gene is a human or not.

Basically, evolution isn't about survival. It's about what genes are more likely to propagate to the next generation. You can simulate this fairly easily: If you have a completely stable population (the average person produces one offspring), and a gene that makes e.g. 10 % of the population produce on average 0.99 offspring, you'll see that after a certain number of generations that gene is drowned out and eventually extinguished. Any gene that isn't extinguished has survived because it doesn't put its carrier at a big enough disadvantage to be extinguished.

Yeah, but I'd suspect that a couple who want a child and has a high risk of having a child with a generic disorder might choose to go with generic manipulation over a natural birth.