At least in my mind, there is no final decision. But I'm inclined to agree with the no subpages point of view.
The only thing that bugs me about this is that subpages are just pages. The only thing that a subpage does that's different from a regular page, is link back to the main page automatically. That seems like a good thing!
Other than that, there is nothing all that special about a subpage.
One of the issues is the ease and naturalness of 'accidental linking'. If I want to casually mention [[Bill Clinton]], I shouldn't need to know that he's really under [[United States Presidents/Bill Clinton]]. But isn't that just an inappropriate use of a subpage, rather than an argument against subpages?
It is true, I think, that every subpage could be just as well titled as a regular page, or put into a pre-defined namespace like talk:.
But I really like the feature where subpages automatically link back to main pages.
Compare:
[[Military of Afghanistan]] and [[Sudan/Military]]
In the former, the author had to link back to the main page by hand, in the latter, it happened automatically.