Walking towards my cabin is not a positive action. Depending on its location, I fairly often pass it on the way to somewhere else. For instance on QM2 en route to the library or CC. Also, I thought the point of the thing was you didn’t have to juggle if your hands were full of children and stuff: if you have to open the door anyway, that makes it even more pointless.
My steward is, I hope, a trustworthy person. I have no problem with him/her entering the cabin when I am not in it. As s/he knocks before entering, it gives me plenty of time to remove myself from view, if, say, I am standing in front of the mirror half dressed.