:::::::First of all, flagged revisions won't be enacted for every article. Like semi-protection, it's on a case-for-case basis. So it doesn't violate the "free encyclopedia" pillar in the same way that protection doesn't violate it either. The easiest way to stop vandalism is to prevent it from appearing. We already have protection for that; flagged revisions are merely another step to prevent BLP issues or vandalism from hitting the main article. If I am not incorrect, the ability to mark "approved" revisions is bundled with rollback. Finally, there is an additional incentive for creating an account in that all users, autoconfirmed or new, are able to see the most recent change, similar to how semi-protection gives an incentive to sign up and edit with an account. ''''''''''