On wiki, you can't stop your opponent's edits. They can wipe out yours, and you can wipe out theirs. If you wind up on the other end of a debate with a Refactoring Wild Man, this can take a lot of energy!
Therefore,:
Make Room For All Viewpoints. Once this is done, your opponent will have a page for their utter nonsense and foolish dogma, and you will have a page for your obvious goodness and correct thinking. And the two of you will have a page to slug it out that will not be overly repetitive, and from which whatever skerricks of signal occur can be easily extracted. And it will be much easier for you to eventually reach a Modus Vivendi.
Or,:
Observe Delete Once Restore Once. If a change you make is undone or if the text you deleted is replaced, leave it. The community will end up choosing the better idea.
Or,:
Use Exponential Backoff Editing. (a variant of Delete Once Restore Once)
Or,:
Reply, don't delete. If you have to alter someone else's content, do it only to clean up personal insults, place into context (avoid off-topic), or consolidate repetition.
Wiki Pedia has a similar problem. See observation in www.weblogsky.com 
(Broken Link: 2008/05/25) (Archive Org link: web.archive.org )
One opinion:
Keeping bad ideas runs the risk of putting bad ideas into newbie heads that otherwise would not get there by themselves.
Don't do it.
Alternative:
Even Bad Ideas Should Be Kept: Let all ideas stand, even if they are bad ones.
Bad ideas should be documented so that others don't repeat them.
Treat readers as adults and let them be the judge based on the replies.
See Funny Wiki Processes | Wiki War
See original on c2.com