Okay, let me try this before this thread inevitably gets locked.
If you are attracted to a certain physical trait(s) of the opposite sex (eye color, ass shape, etc.) and especially if it happens be one of the main reasons for your decision to proceed in a relationship,
This is the core problem with your argument, imo. In my younger days, I might have asked a girl out because she had stunning eyes or a great ass. But when you start considering marriage and children, those things really become superficial. It's about your connection to the person. And that can't be faked with plastic surgery.
If you're saying something like, "I want to have kids with her because she has green eyes and a shapely ass and I want to pass those traits down to our children," you sound,
at best, like a Vulcan from Star Trek.
Your sickle cell argument was better. I get why you don't want to follow that line of conversation, but combining traits that might harm the well-being of the child is a more valid reason than, "I should be able to reasonably expect that my child will have green eyes."