To get around these philosophical issues, I believe
that the only way
to measure quality of articles (especially contentious ones) is
qualitatively, ie by asking people/experts their opinions of articles,
their experience of the community etc and analysing the types of
reactions, the emotional resonance (or lack thereof), the language
they used etc. So far, I haven't seen many qualitative studies of
Wikipedia - I did one last Christmas as a kind of pilot study for my
dissertation, which you can see here:
http://wikisource.org/wiki/A_small_scale_study_of_Wikipedia
and some others, from Wikimania, include:
http://en.wikibooks.org/wiki/Wikimania05/Paper-PA1
http://en.wikibooks.org/wiki/Wikimania05/Paper-JT1
Note: almost all Wikimania papers are still works in progress, including mine :)
He shows that the number of authors is the most important variable to
predict the quality.
Jakob