I believe that under most circumstances a user's main userpage [[User:X]] should be a place for that user to state what they want the community to know about them and their beliefs, philosophies, aims, goals, etc. In other words, the main User: page is intentionally POV and there should rarely be a need for other contributors to edit it.
It is certainly NOT a place for other users to place their opinion of that user under normal circumstances.
However, all this is accomplished with the current state of affairs. User pages are indeed rarely edited by anyone but the user. There are rare cases of vandalism, quickly undone. Few users' pages are regularly vandalised, and those pages can be (and are) protected under our current policy.
It strikes me that some of those wanting their user pages protected from editing by other users are not doing so out of actually experiencing any problems, but rather, as UC says, from a sense of 'ownership'. This IS a bit troubling. Certainly userspace is different than other namespaces in the system, but it seems to me that the 'Wiki way' is to avoid trying to fix problems in software whenever possible - instead relying on community norms and consensus to set de facto policy.
'If it ain't broke, don't fix it' is the rule of the game here, I think, and I haven't seen sufficient argument that the current state of affairs is so broken as to override the objections.
-Matt (User:Morven)