What if those downloads were by people who already paid to see the movie in theaters and downloaded it later to watch it again?

If they waited for the DVD or Blueray to be released they could watch it an unlimited number of times after paying once. Should each time they watch it at home on a legally purchased DVD be considered a lost theater sale?

Well, actually, from what we've all seen, MPAA and RIAA like to ask for much larger penalties than that; sometimes thousands or tens of thousands of dollars, per violation.

No, that would be much closer to a reasonable penalty than they attempt to incur.