Wikis work because they rely on the community
(Thats you and me folks), rather than technology, to police itself. If someone comes along and deletes text or posts spam, someone else can just as easily fix the problem. Since an open environment encourages participation and a strong sense of community, the ratio of fixers to breakers tends to be very high, so the wiki stays stable :) nice isn't it ?
There are technological protections, too -- they're just less obtrusive than having to "log in" or "rate" something. Most wikis store old versions of each page for at least a short period of time, allowing damage to be easily recovered. Many wikis provide a means to limit how quickly someone may edit a large number of pages. Most wikis also provide a means to lock out particularly abusive visitors without disturbing other visitors. [WikkiTikkiTavi]
provides all of these features.