The discussion covered both cosmetic changes (like eye color) and health defects (such as handicaps and vision correction). I did not see any distinction drawn between the two during that discussion.
Beside destruction of embryo, even in therapeutic use we should distinguish between a health defect and cosmetic improvements.
What would be the problem with making a genetic change, for cosmetic purposes, to a naturally conceived zygote? Is it the child's lack of choice that makes it immoral, or is it the change itself that is morally problematic?
If it's the cosmetic change itself that is immoral, does this also mean it would be immoral for me to shave every morning and afternoon of my adult life? Or for me to get some kind of advanced permanent laser hair removal? (Assuming that it was for purely cosmetic reasons and there was no health necessity for being clean shaven).
I see a difference here in genetic manipulation of a zygote versus shaving laser hair removal.
I think that the change itself is morally problematic absent some disease. Therapy means that something is broken as compared to the divine design. For example, a heart valve is not where it is supposed to be. Cosmetic is when the human parent wishes to alter the design alrady given the child, for example stature or eye color.
When a human being is groomed, e.g. receives a hair cut or a shave, there is no interference in the design. God gave us tools with which we groom out children or ourselves.
It is sinful to interfere in the act of creation. It is not sinful to remove and obstacle, such as a disease, even on some stage of creation, or to alter appearance of the finished product, such as grooming.