Yes, he simplest solution would be to ban all boxes not related to Wikipedia or your activity on wiki (such as babel boxes). Though it's pretty easy to tell what's divisive and what isn't (which, I think, is a reason to speedy delete).
Pretty much anything can be divisive. Some things are obviously divisive, but there are plenty of less obvious things that some people will be offended by (often legitimately). To use the example already given, supporting the US/UK/etc. troops in Iraq could very easily offend those Iraqi's that are angered by the presence of foreign troops in their country. It's all too easy to dismiss something as not being divisive just because you don't personally know anyone that have strong feelings against it. Because of that, it's best not to even try and just ban all such userboxes.