Some things for your consideration from someone with experience with decisions like this:
The ones who are horrified that you'd euthanize a chick because of such a defect are not going to have the responsibility for that chick and have no right to push someone to keep an animal like that, no right to guilt someone else into doing what you think is right in this type situation.
I have a crippled rooster, Zane. He's been unable to use one leg since he was six months old--he is now 3 years old, lives in his own cage, has to be taken out on sunny days, but can't be left completely alone because he would be hawk bait. We worked for months to kick out an infection in his injured hock joint, and finally did, but he has no use of the leg, which is in a permanent bent position and the toes do not flex. He thumps around on his good leg, using his wings like crutches.
Would I try so hard to fix another one like Zane? No. We tried so long to help him and get his leg functional again that it was impossible to put him down. He showed that he was interested in life still because he can see, he can hear, he can alarm for the girls, and he crows when he feels good, so we decided to care for him till he didn't want to live or till he became ill. It takes thought and consideration every single day to remember to do things for him that he cannot do for himself, like pick up grit for him when he can't get outside on the ground, to trim his toenails since he can't wear them down, to keep the spurs short so he doesn't gouge himself, to dust him with DE because he cannot dustbathe, to bring his girlfriend, Gypsy, to see him so he feels like he's still alive, etc, etc. I adore him and he's super affectionate, but he deserves a more full life.
Blindness would have made my decision so ever much easier. I have euthanized a blind chick. I now have a sight-impaired hen, but she can see. Her depth perception is way off and she can't aim to pick up anything very well. BUT, she can see. If she had been blind, I would have euthanized her, no question. The question of quality of life is what the OP needs to answer, if it's even possible to know if it has any.