The case with gay genes is different. Regardless of any other trait, I'm genetically prone to not have any offspring. Thus, eventually my genes would be less and less common.
All that's required for a trait to persist is that it benefits the pool.
If the pool benefits from have 1% of members being blind, then so they shall be.
We don't have to understand the benefit for it to exist either.
Or that it's less bad than whatever beneficial trait it's coupled to.
Humans consume a lot of water in order to shed heat. Our backs are pretty f-d up. Our brains waste a lot of energy and require a very long childhood. But on the flip side we're basically terminator compared to the African fauna our primitive ancestors hunted.
From Wikipedia, quoting evolutionary biologist Jerry Coyne: "Group selection isn't widely accepted by evolutionists for several reasons."