This is only true when there isn't enough information supplied. You can't expect the doctor to figure out what the problem is just by telling the doctor you have a pain in your side, same goes for the lawyer's scenario.
No offense to doctors/lawyers meant here; all human brains suck at that.
The confidences here provide misinformation. This is more harmful than no information.
The doctors job is to provide me with as much information about the objective criteria of my physical condition as possible. However when it comes to making choices about my treatment, say in the case of accepting/rejecting an experimental drug with some potentially nasty side effects, it should be entirely my own value judgement on what to do with said information.