Your example about the debate of BN usage demonstrates that it is possible to look inside a deep network and debate. That we don't know the answers doesn't mean the answers don't exist, or are impossible to find, which is what the term "black-box" suggests.

Of course, more research in tools for model interpretation would be awesome, and my own lab has done a lot towards it, and this remains an important topic. More is desired, but what we have right now is pretty good too, and is not at all inferior to old-school methods, esp. considering the performance.