I'm not quite sure what good and bad or right or wrong have to do with anything and why I can't apply my worldview to my reality without a definition of either?
As you said
Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle. That principle is of great antiquity; it is as old as Socrates; as old as the writer who said, 'Try all things, hold fast by that which is good'
You have to define what is good before you can hold fast by it.
Edit:
On a second look perhaps the quoted author is merely throwing that sentence out there as commentary? Maybe it is this that is the heart of the matter.
it is the foundation of the Reformation, which simply illustrated the axiom that every man should be able to give a reason for the faith that is in him, it is the great principle of Descartes; it is the fundamental axiom of modern science.
Yet as we see in
The Limits of Science reason cannot ever answer all questions. Faith without reason is impossible to avoid. The apriori cannot be escaped.