ETA: There is at least one other reasonably courteous person in town! As I was getting ready to go, a guy by himself sat down at the 4-person table next to me that had recently been vacated by a couple, then got up again, saying to the server clearing it off "I don't want to sit here and take it up when others might need it." I told him I was leaving so he could sit at my table, and he asked me if he scared me off. :) I reassured him that I'd just finished my lunch and was leaving anyway.
You can comment here or at the Dreamwidth crosspost. comments at Dreamwidth.