Are you referring to black spots on the banana peal? Black spots on the peal indicate that the banana is getting ripe. If the banana is completely black then it is likely not very good to eat.
When eating bananas it is important to use your nose as well as your eyes in assessing it’s edibility. As long as the inside of the banana looks and smells good, I’ll eat it even if the entire peal is black. Black is sometimes still beautiful.
I think that people who can’t stand to eat a banana with any black spots on the peal are people who simply don’t like eating bananas.