Wikipedia already stuffers from variable quality, and all its content comes with a big huge caveat emptor. Furthermore, the existence of poor quality doesn't have any bearing on whether the well trafficked content is good or not.
Deletionists really don't have any leg to stand on, and i find it mystifying and infuriating that they are allowed to continue deleting content put up by other people (mostly in good faith), essentially without cause or justification.
They can't delete their way to good content, because no content on wikipedia starts out as good content. You can't claim that leaving up poor content is a problem, or they should just lock the whole fucking thing, and only accept well curated patches.