I think you explained some of this last time it came up, but thanks for the refresh and the details. The Edit with new information about the moons is very relevant and fascinating. I think the debate about ethics tends to fall into the philosophy category (one of several paths, probably), and that's how I'm looking at it. While I don't disagree that the mission is well worth undertaking for the sake of human knowledge, the argument is premised largely on involving economics with the ethical considerations ... thereby making it a "human justification". I understand that the impact to Saturn seems immeasurably small and insignificant to us, and is therefore worth the risk for our potential gain, but it's really interesting how shifting the equation to the moons makes a world of difference in our 'concerns' and motivations. I guess you could say "size matters" in this situation.
Perhaps an old science fiction parable has stayed with me all these years. I can't remember the book, but I think it was a classic sci-fi (Land of the Lost?). The premise was that scientists had found a way to time travel back to the era of the dinosaurs in order to study them. They had specific rules about the research method, and a special "pathway" IIRC they would walk on in order to not alter the environment. So on one journey, one of the scientists inadvertently stepped on a butterfly that had careened into the pathway. No big deal, a drop in the ocean, right? Well, when they returned to their own time in modern society, everything had radically changed. At first they were mystified and dismayed ... had they returned to the wrong time rather than the exact moment they had left? What happened? Then they came to the conclusion that stepping on that butterfly had changed the path of evolution and destiny, by a tiny amount in the beginning, but over the course of 65 million years that tiny ripple had expanded and made some impact on the course of human evolution and human history. There seemed to be a moral/ethical lesson in that which impacted me as a rather young lad. Some believe that "everything is connected". Maybe this is what I was referring to, though I haven't located which book yet:
Ray Bradbury took a different approach, and essentially invented what chaos theory 20 years later named ‘the butterfly effect.’ … [His time travelers] are required to stay very carefully on the trail, and not disturb any living thing, because it is understood by the masters of time travel here that there could be unexpected effects in the future. And sure enough, somebody clumsily steps on a butterfly, and as a result the presidential election [in the future] is changed for the worse.
Ha, it's like we're actually living that now.
Anyway, if Star Trek is ever going to happen, we'll need plenty of 'justification' and an airtight Prime Directive. I'm curious which sci-fi book that was BTW ...