Some people might find that certain MediaWiki sites such as Metapedia, Encyclopedia Dramatica or even certain parts of Wikipedia offend their moral standards. But there's not much that we can do about that. If MediaWiki were proprietary software, the organization owning the copyright could refuse to allow certain entities to use it. But the MediaWiki community is rather powerless to influence how people use the software, because the licensing allows it to be used for any use. Even if we built in code to enforce some standard of morality (e.g. installing porn filters similar to Google; see http://en.wikipedia.org/wiki/Safesearch), anyone would have the legal right to remove the filters and to distribute the modified code, or to create a patch to disable the filters. Therefore, morality is mostly outside the purview of the MediaWiki community. On the other hand, if someone wanted to put Extension:PornDistributor on MediaWiki.org, or if someone wanted to link to Pornopedia from http://www.mediawiki.org/wiki/Sites_using_MediaWiki/en, I guess disputes about morality could occur, but so far that doesn't seem to have happened.
I think the best thing for those who are offended by certain content to do is to improve code such as http://www.mediawiki.org/wiki/Extension:ImageFilter so that it will be more feasible to create mirrors of various wikis that allow users to opt out of viewing content tagged as adult, sacrilegious, immoral, or whatnot. The openness of the software and the content is beneficial in that it allows people to tweak it as needed to suit their tastes. Then of course there is always the possibility of buying third-party web-filtering software.