But the answer to this "why?" is just super boring: it's because people don't like unorthodox views (that's what makes them unorthodox). It's not an enlightening answer.
> I think public justification of downvoting/flagging would help him in his job & make his job more rewarding to him.
I do think requiring a rationale for a flag is a good idea. I don't think so for a downvote.
The "solution" for downvotes is just to not worry about it so much.