Please, harsher penalties for bad players.
Yeah, and trolls/flamers who go ballistic at friendly advice. I'm not one of those people who sits back and orders other players around and thinks typing in all caps will fix everything. In fact I can't stand them. But when you leave me, only in mediocre PvP gear, alone to guard a turret by myself, and act like a brat when I suggest that it's pointless to leave one guard (time and time again I've seen this---one person stays behind to call out "incoming", which is all but useless by the time the enemy team storms the spot and grabs the turret), it's pretty annoying. When you get a turret, don't give it up so easily, unless it leaves another one poorly guarded by the enemy. Pretty simple.
As for the penalties for bailing, though, I don't think that's the best idea on it's own. Won't that just encourage the wrong sort of unmotivated, poor team player to stay in? Let them bail and someone who actually helps out replace them. Yeah, maybe ideally game mechanics could force people to stay and do what they should be doing, but for some players you just have to leave room for replacements instead of discouraging them.
EDIT: I love the above idea. Positive reinforcement which has a lot of room, as opposed to negative which is limited in how far it can go.