Personally if the drop in/out system works than I have no problem with people quitting. if I am stuck on a lame team and have to carry them, I will quit too. No point in me doing all of the work. If something happens outside of xbox (real life) than you should not be punished for quitting. If you are stuck with lame players than you should be able to quit.
In CoD, if I am losing or carrying the team and losing I quit, its not hard for other players to join the team I quit and not hard for me to search for another game. The whole point is to have fun, if the game sucks, than leave. I hate when i get paired against a stacked team and they dont do the objective and just kill, it makes the game no fun, so i quit. I dont care