I find it hard to believe he "literally" has no brain. I'm sure there's at least some vestigial organ resembling a "normal" brain somewhere in there. Is the kid literally brainless, or are we talking something like Down Syndrome, where it's a chromosome issue? I've lived with several close people "suffering" from Down Syndrome and I tell you not for a single solitary moment would I consider sacrificing a person because he or she suffers from it. On a general note, cases such as those mean you lead an awkward social life (as well as need constant care from others to properly survive) but it doesn't undermine the preciousness of their lives not one iota.
Being literally "brainless", on the other hand... well, if such is the case (the video doesn't make it too clear)... you wouldn't even be sentient to begin with. Screw social faux pas and needing care: you would have no sentience, no knowledge or awareness of life, no memory storage, no personality growth. You would never enjoy nor suffer. You would be technically alive and that would be it. People in a vegatitive state, or a comma, or paraplegics would enjoy a better quality of life.