Why Non Liberty books on a liberty site? In order to be a great champion of liberty there are three main reasons to read non liberty books:
Liberty authors are not infallible and reading our opponents, it will be easier to find and fix our holes
Just like liberty authors are not infallible, non-liberty authors are not completely fallible. They are correct in certain cases. It is important to know these areas and how they relate to libertarian ideas.
Someone can be intellectually honest if he argues against a point that he/she is not willing to understand.