So, you are worried that he has a mental deficiency that might render him less than adequate at 1B. Others are worried that maybe he lacks the work ethic. No one knows which if either it might be, but apparently both have noticed behaviors that are concerning. You say that those who think he isn't trying are engaging in character assassination, but you seem to be wondering whether he is just an airhead (aka a dummy). Neither characterization is flattering, so you shouldn't be throwing stones.