To call him a retard is to strip away at his humanity and lump him into some inferior group.
Ever read Animal Farm? "All animals are equal, but some are more equal than others." That's basically it.
Someone has decided they are more equal than Grayson.
Grayson is equal. He doesn't need or deserve to be dismissed. God, or Nature, chose him to be born, just like anyone else. He made it through...he's here like everyone else. He deserves his dignity and his responsibilities, too.