Is there anything to prevent a saboteur from deleting all the text on a page?
No. See WhyWikiWorks...
You can actually go further and wipe out most of the page database before anyone notices between page deletion and RecentEdits. There is no peer reviewable procedure to recover from this on this wiki.
While this was once true, it is no longer. See HistoryPages. Many other wiki engines, such as UseModWiki and WikkiTikkiTavi, implement some form of KeptPages. For WikiWiki, there are external backups available too. [Which makes them more attractive for WikiSpammers, because the KeptPages boost the PageRank of external links. Even spam deleted from WardsWiki, for example, still is indexed by Google and helps the spammer pay his bills.]
The question above is of course one of the most frequently asked, and the response is shocking to many people.
In the earliest days of multiuser and networked computing there were many people who did not believe in passwords or other security measures, usually in academic or research communities. (The MIT computer labs had an especially strong open-system tradition, with unusual solutions to the social problems. One example was a crash-system command--it took away the enjoyment of figuring out how to crash the system.) Another open system is Usenet--even today there is only limited protection against vandalism, yet Usenet is still popular.
The Internet has ironically closed many of the last open resources, since policymakers required at least basic security measures for Internet-connected computers. (In one famous example, RichardStallman was given the choice of using a password (more than 0 characters) or losing his MIT account. He chose to set the password to "rms" and tell everyone.)
It is still an unresolved (open? :-) question whether Wiki will survive--many other open communities have closed, ceased to operate, or simply failed. (See many of the WikiWikiClones for examples.) Several people believe that the Wiki community here is fragile, and would not withstand major exposure (like the dreaded SlashDot Effect).
In any case, the Wiki is open and alive right now, thanks to the many people who have worked to build the community.
Little by little the world advance. OpenSource, GPL, wiki ... one day we will all work together.
--NO!!! (by The Individual Anarchist)