Well, I'd argue that they should either all be banned or all be allowed - with only specific guidelines, if any, on their actual content (like profanity, images, whatever). Userboxes can serve a useful descriptive purpose and contribute to the task of building the 'pedia by giving you useful information on the editors with whom you work. If you say 'Delete all the ones not related to Wikipedia' then you just shift the arguments into a new pattern without really changing the dynamic. We should accept that we will never all agree on what content is appropriate or inappropriate in userboxes, accept that userboxes have some utility to the task at hand, and agree to squash future drama associated with people objecting to others userboxes.
They are usually not on the talkpage; they don't interfere with communication; having a userbox is descriptive and doesn't change who the editor is or what they believe; you can just ignore them and ultimately knowing someone is a pedophile is better than not knowing.
Nathan