When I first started this topic, I didn't expect the discussion to go this way. My request was really simple: if you were kicked for running out of time, you don't get to give an expressed opinion on someone i.e. you cannot give a green or red thumb for that game.
The reasons behind this is fairly simple:
a) the player who ran out of time are generally at fault in the first place. In a tournament setting, the player who ran out of time loses by default. In BGA, we allow the option to give the opponent a little leeway, but this shouldn't be taken for granted.
b) to prevent the player from retaliating the player who kicked him with a red thumb. this is very unfair against the player(s) who had waited 3 to 7 minutes (or more for kinder players) and yet still get a red thumb in the end. Some form of "protection" should therefore be put in place.
I generally only give red thumb to player who is rude (language wise). I'm pretty sure some players here give red thumb for various reasons such as:
a) to rude players
b) to players who doesn't respect the spirit of the game (like table talking in hanabi)
c) king-making (these players should be reported!)
d) slow players
e) quitters (this is different from conceding a game because quitting in a multiplayer game might affect the result in the end)
f) conceders (I personally think conceding a game is fair but I can agree to disagree here)
g) just being a sore loser
The karma system that sourisdudesert proposed only helps with problem (e) and (f). Besides that, we already have got the penalty system which is directed for problem (e). Therefore I think this karma system may not be that helpful in replacing the thumb system. A nice way to implement this system is to add another feature on "recent penalties" with a white flag symbol to show the number of games conceded, maybe?