Firstly, there's the issue of inflamatory userboxes. It appears that userboxes supporting American troops in Iraq are acceptable, but userboxes supporting the Iraqi insurgensy aren't. Userboxes supporting the killing of Iraqi insurgents are acceptable, but ones that support the killing of American troops aren't. Surely both the "support" ones should be acceptable, whilst the ones that support killing should be delete. Then there's the ones that advocate peodophilia. Users who have these often argue that we accept homosexual userboxes, which is just a stupid argument, but they don't seem to be able accept that.
The answer is, of course, to ban all such userboxes and be done with it. Trying to decide what it is and isn't acceptable to express support for is just asking for trouble.