The option to quit when you are loosing, getting bored fighting an uninteresting and uphill battle or have to go for whatever other reason, should exist.
On this i think everyone agrees. So the problem with "Rage Quitters" is not a problem with people leaving the game, its what happens afterwards.
Now, as the game is designed to go on, replacing quitters with AI, so that you have to fight to the end to actually get the win, here is where the problems start.
This logic can be understood if for example there are several players on one team, and only one have to go, or want to quit. This allows the game to continue with AI, giving the staying player at least a chance to win. This i approve.
However this is not what annoys the most, the real problem kicks in when everyone on one team have quit, and the humans are forced to still fight for another 10+ minutes just to get the win, vs AI. This is the real design flaw. It is very boring and uninteresting to play "comp stomp" games if you are a competitive player, these kind of games are not what is sought for "multiplayer games" and have no place here. If one have the urge to play vs AI, there is the single player option for this, or even custom games if human allies are wanted. In competitive games as pantheon/skirmish modes offers, there should always be the option to "Victory!" as soon as all the humans have quit on the opposing team.
Just look at how this is done in all other major RTS games, (blizzard *cough*) and you will see what i mean. This solution is really the optimal one, and was invented over 10 years ago. And for how much Demigod does right, i cannot understand how these kind of small, unlogical, and greatly flawed design decisions exist.
There would be no complaints on "Rage Quitters" had the tried-tested-and-approved way to do it been used.(giving the "Victory!" popup after last human player on one team quits)