quiting from a free for all game isnt that really big of a deal. niether is quitting from team games on the level of team swat and team snipers. my personal belief is that these are the ONLY playlists you can quit from and not really hurt antone else.
however, quitting from team slayer, squad slayer, arena, mlg, invasion, etc. should be HARSHLY penalized. in invasion, you need to tactically place yourself to spawn your team as close to objective as possible. when a person quits, this balance is disturbed. i had a game where i couldnt spawn on a team mate simply becuase he left the game. i had to spawn at the default spawn points -.-
also being outnumbered in an objective style game, where number is a key advantage, is bad. unless you team are gods, or neither team is smart enough to go for the objective, neing outnumbered by 2 or more people can prove to be a disaster.
people who quit these gametypes need a severely harsh penalty. if it were possible, they should be completely banned from playing any reach at all for the next hour or so. they hurt thier team by doing this, so they should suffer as well. an entire ban from reach might do some good, but my only concern is whether or not its possible.