In general, its been principle to keep things open, open, and open, though probably nobody would complain if you became a sysop and protected your own subpages.
Actually, they would. Protection is meant as a defense against persistent vandalism, not as a reward for admins.
If you want a non-editable page, please don't use a wiki. I see no reason user pages need to be protected any more than any other page. You don't own these pages just because you created them in the user namespace. See http://en.wikipedia.org/wiki/Wikipedia:Ownership and http://meta.wikimedia.org/wiki/Protected_pages_considered_harmful.
Angela.