Also rating with “stars” is very unclear. For example, in many contexts (e.g., amazon marketplace, most movie ratings, etc.), a one star rating a bad rating (essentially a downvote).

Actually we could do exactly this! Remove totally the down-vote button since it is clear that the first star is ALWAYS a negative vote, I can't think of any example where it has positive impact.... so we could for example: (please elaborate further)
1 "star" = -5% down-vote
2 "stars" = +5% up-vote
3 "stars" = +25% up-vote
4 "stars" = +50% up-vote
5 "stars" =+100% up-vote
no vote = neutral

that way(logarithmic) we are more "positive" weighted... we don't have the the negative psychology about down-voting but still "indirectly" (without knowing it) the community practically still down-votes bad content... (yep, facebook has a strong reason not to have a dislike button, we don't need to invent the wheel again and make costly researches when others already have do it)