Earlier you made the following statement:
Rule #3: All security is ultimately "security through obscurity."
That is what is under debate. Is it true that all security is "security through obscurity"? There is a difference between understanding how an encryption algorithm works (obscuring an algorithm), and knowing a particular key to decrypt ciphertext using that same algorithm (obscuring an input to that algorithm).
For instance, it is possible to understand how the Diffie-Hellman algorithm works works -- meaning it is not obscure -- and yet still be unable to decipher the contents of a message encrypted via that algorithm. In this example, as in many others, the workings of an encryption algorithm need not be obscure in order to be considered secure.
In the sense that algorithms rely on their inputs, such as private keys, to be kept hidden (obscure), you would be correct. But since the phrase "security through obscurity" typically refers to the algorithm, and not its inputs, it would be misleading to claim that all security is "security through obscurity".