I'm sure all of you have experienced at some unfortunate point where a player has entered your game and immeadiatly proceeded to kill all of you before leaving. This ruins progress and the fun vibe of playing L4D. I suggest there should be harsh consequences when players do this, like server bans or in the most prolific cases, Steam bans.
I must stress I am not saying that accidentally shooting a team-mate needs a ban, just the senseless action of entering a game, killing all players and then leaving must stop.
I enjoy playing on Steam and find the community to be very helpful but we must act to stop this.