SilentKlD, I 2nd your reaction to the polite zombies, as well as your suggestion that they should open doors just by staggering into them, and then not bother to close them.
Sotha, I appreciate your points. They can be addressed by doors that automatically close after some time delay, which I've seen in some missions. Auto-closing doors also address your points for the case when the player leaves a door open, plus the case when an AI opens a door and doesn't shut it because the player sidetracks them. However, in my opinion, timed auto-closing doors are immersion-breaking as well, especially in missions that aren't supposed to be haunted. I have a humble suggestion.
It is possible to make auto-closing doors completely natural and non-immersion-breaking. Many real life doors are auto-closing, and I'm not just talking about the ones with a spring mechanism at the top. If the hinges are misaligned vertically, the door swings shut under its own weight. I'm sure everyone has noticed countless doors like this, especially in older buildings. If the misalignment is slight, it can take quite some time, say 5 or 10 seconds, for the door to close all the way. Also, you will notice the door starts moving extremely slowly, and then accelerates, reaching its max speed just before closing all the way. This is the perfect behavior for a self-closing door in TDM, because it leaves the AI or the player plenty of time to go through the door while it's wide open and moving very slowly, even if the player is crouched and/or creeping. If the player sits in the doorway and the door does hit them, no big problem, it just stops, and then starts to swing closed again once the player leaves. This way, TDM could have self-closing doors that are completely natural. And as a bonus, zombies don't need to be polite with doors, just stagger into it to open and then leave it to swing shut on its own.