They cite scripture all over the place.
I'm not sure why you think that an encyclical which gives a reference to a particular writing by a particular church father or saint has to reiterate and explain his entire argument.
The only thing that has the kind of "he said it, therefore I believe it" authority you're talking about in the Catholic Church would be Scripture, and the infallible pronouncements of Councils and Popes. The writings of Augustine are neither of those two things, therefore, anything Augustine wrote is valid only insofar as it does not contradict those sources.
An argument has no authority because it comes from Luther or Augustine. For authority, it need to comply with scripture.
An argument has no authority because it comes from James White, either, yet you cite him.
By the way, who is qualified to judge whether Luther's, or Augustine's, or White's argument "complies with scripture" or not ... and who gave that judge that authority?
“An argument has no authority because it comes from James White, either, yet you cite him.”
I quote his ARGUMENT. Agree with it or not, it is his argument that I’m interested in. I don’t expect anyone to be impressed by a name, only by whatever valid thought lies in the argument.
I’m pretty sure James White would reject the idea that his words have authority, apart from their compliance with scripture.