A beaker full of death wrote:
One point of view would be the prime directive is subject to constant change.
In TOS it wasn't some nebulous philosophy. It was a codified military regulation. General Order #1. It had specific rules for what to so and what not to do. McCoy and Kirk quote part of it in Bread and Circuses.
What's interesting... and what we'll never know, is how does the Prime Directive relate to a Captain who is put in the unenviable position of dealing with a prior contamination? What type of latitude does he have in correcting the prior contamination?
Kirk does seem to have pretty broad authority in A Piece of the Action