After trying out the no-pvp server tonight, I realized that there is far more griefing going on there.
Another player was able to break my door and build his own in its place, effectively trapping me inside. At first, I attempted to break down the door while he repaired it from the outside. In the end I waited him out and he got bored, knocked down his door and put my own back in its original spot.
I suggest that users have ownership on doorways just as they do with doors, so that an aggressive player must use c4 to knock out the doorway before placing a new door of his own in the established building.