I think the original Prime Directive from TOS was fairly straightforward. A statement about the U. S.' involvement in the Vietnam war. Another, "In the future, we don't do that kind of stuff anymore." Storytelling in Star Trek evolved and expanded over the years. I think this has left the Prime Directive still valid, but vague.
Vague in the what ifs of not intervening to prevent the destruction of a civilization that isn't brought on by that society's (or societies) decisions. I get if the Federation sits out on stopping a society its own self-destruction. Even if new to warp technology, a planet with societies bent on self-destructing means about all the Federation could do is become the planetary police force. I think SNW's s1e1 planet Kiley 279 is an outlier. Kiley 279 being on the precipice of warp-backed absolute destruction was Starfleet's fault. Unintentional, but still their fault. I think violating the Prime Directive in that situation was warranted.
The Prime Directive is like the rule to stop at red lights. Not an extensive treatise, but important. Violating that rule can lead to very bad things. Still, sometimes following the Prime Directive can lead to very bad things, like in the Terran universe. I wonder what would happen if that scenario was repeated in the regular Star Trek universe. I think the First Contact Protocol is a lot more extensive and comprehensive. There's a lot of possible first contact scenarios, from "hey, cool, welcome!" to panic and attacking the landing party.
The Prime Directive is important. However, I think it isn't comprehensive.
More rules=more opportunities to let criminals through without consequence. If you have rules A,B,C,D,E,G,H,I.. Someone could reasonably say "You were so thorough, the omission of "F" had to be intentional".
A B&W guideline, with the understanding that the letter can be violated at the cost of a thorough investigation afterward is a reasonable approach if everyone acts in good faith.
That's an interesting perspective. I agree that "this is a set law" can be perceived as anything not covered being construed as legal (although not necessarily moral). Which could lead to the creation of a new law, or the change in an existing law, to cover the new territory. I also agree that with a guideline a lot depends on acting in good faith. I think the Prime Directive is vague when the situation is the destruction of a civilization due to a natural cause, not from the actions of the civilization.
Say a natural event -- a meteor or asteroid or solar flare or something -- will cause an extinction level event on the planet with a pre-warp civilization. And, Starfleet has the means to prevent such a thing. As long as the pre-warp civilization never knows that their destruction was prevented by Starfleet, whether choosing to save the civilization or to doing nothing and allow it to be destroyed, are both following the Prime Directive. For me, that's where the Prime Directive is vague. Or, quite likely, I'm unsuccessfully trying to process two vastly different outcomes having the same value, i.e. not violating the Prime Directive.
The Prime Directive is not a bad idea when it exists to minimise harm.
When it gets turned into a pseudo-religious dogma, where it is considered better to allow a culture to be extinguished than to risk contaminating it, that's when there are problems for me.
Zero tolerance policies ensure injustice in outlier cases. Yes, it’s unethical to interfere in a civilization’s development 99.9% of the time, but there are always exceptions. Ignoring outliers is pretending your system is above the fundamental laws of the universe.
My biggest (only real) gripe with it is the "sit by and watch a civilisation die from something we could prevent inside five minutes without ever being noticed" shtick.
My theory -- based on us seeing numerous violations of the Prime Directive from main characters -- is that the interpretation of the rule is "you better be willing to risk your career if you break this," not "your career is 100% over if you break this."
It's a heuristic, and a good one, but there seems to be in-universe exceptions for exceptional cases.
I think it really just boils down to that notion that it's better to let a civilization die in a preventable natural disaster than interfere with their "natural development".
Aside from that absolutist take, there seem to be plenty of exceptions to the PD - Starfleet is free to respond to distress calls, consider individual requests for asylum, offer assistance when a planets government asks for it, etc.