There are already other mechanisms in place to distribute Emacs code, like any of the Emacs package managers and Git, and yet EmacsWiki continues to be a place where code is collected and discussed.
I don't think moving to another wiki system would change that, since any other wiki system would have the same shortcomings as OddMuse in this respect. There is a straight trade-off between maintaining security on wiki pages and their utility. OddMuse does a good job, like all wikis, of keeping a page history that allows all edits to be audited. A new wiki might prevent editing of the code, or only allow editing by "verified" users, but that still provides no real improvement to security, since anyone can sign up and post code. Neither, incidentally, does a Git repository like GitHub or Gitorious; if you're unwilling to read and understand the code you download, you still have to put your faith in folks you don't know. Even if you do read and understand the code, you still can't be sure.
More importantly, however, is your implied assertion that security is a problem in practice. Have there been any cases where malicious code was posted on EmacsWiki? Did it cause harm?
I'm getting the feeling like "publicly editable code" is a manufactured issue to be divisive, but I could just be unaware of a security problem that has been pervading the Emacs community.
He's right; community code is a model that works on Github and absolutely does not work on an unauthenticated Wiki.
At least I'm pretty sure I don't have many emacs packages that originally came from a file on Emacswiki...