Unfortunately, we still get messages to the help desk and through other channels from people who come across a high-profile article when it's in a vandalized state. The most-viewed pages are attractive targets for vandals as well as honest readers. If you keep those unprotected more people are going to see the vandalism even if it's reverted quickly. If these articles are protected, vandalism is still easy to spot by vandalhunters but not so much by the casual reader.
Mgm