I got this idea from StuffOfInterest (see User:StuffOfInterest/Userboxes), after looking around to figure out why my atheism and moral realism userboxes got changed from endorsements of the two ideas into the milquetoast "this user is interested in...". I think the rationale for NPOV is an absolute must - for encyclopedia articles. NPOV is inappropriate for userpage content though. See User:StuffOfInterest/Userboxes#Userbox_war for the details on the uprising of would-be userpage-NPOV enforcers.
For individuals speaking for themselves to be prevented from expressing points of view, would make Wikipedia worse off. Expression of personal points of view on userpages helps others better appreciate your perspective on your edits; more importantly, it helps Wikipedians get to know one another and fosters a sense of community, rather than faceless anonymity. Besides, no one is fooled by the supposedly NPOV-ized replacement userboxes indicating that "this user is 'interested in' atheism", "this user is 'interested in' Christianity", etc.; we all understand the expressions of personal points of view inherent in those milquetoasted userboxes, though we must do so with the annoying mental step of de-Orwellianizing them. Wikipedia is privately owned and so can offer whatever services or prohibit whatever expression it feels like on its servers. However, expression of personal points of view is inherent anyway in any userpages, messages to other users, or discussion pages. I don't think efforts to prevent Wikipedia servers from being used to convey individuals' personal points of view in userboxes are meaningful unless they also do away with userpages, user talk pages, and article talk pages.
