"Shaming" quitters isn't the right solution, since, as Per mentioned, many people don't think it's a bad thing.
In practically every strategy game, you'll notice that more casual gamers don't like quitting because they find the satisfaction of destroying the enemy more important, while more hardcore gamers (whether in StarCraft, chess, or similar games) don't like people who don't quit, since it's wasting time they could be spending on playing their next game.
Liquipedia provides one summary:
http://wiki.teamliquid.net/starcraft2/BM
Not leaving the game - When you know you have lost the game, you should leave. Dragging out a game by not leaving is both annoying and rude to players and observers.
Players will of course have preferences, but I don't think the game itself should have any bias about which is better.