This is what I mean by the TOS version of the PD versus the TNG version as while the TNG version made it apparent that what Kirk did would be a violation of the Prime Directive, the TOS version only seems to cover not screwing with pre-spaceflight planets, they never said anything about it affecting dealings with species they already made contact with who the majority of which knows they're from outer space.
On the contrary, they said something about it in "Friday's Child" itself. "And the highest of all our laws states that your world is yours and will always remain yours." It was made quite explicit in that very episode that, regardless of whether a society had been contacted or not, the Federation respected its right to self-determination. It's not about spaceflight. It's about not being cultural imperialists, about being humble enough to recognize that other cultures are better qualified to know what works for them than you are, and have more of a right to make decisions for their own society than you do.
Given what we know about Kirk, I'd agree that his motive was probably guided more by his morals than by politics. We also don't know for sure if his attitude towards this law was atypical in that culture. Look at the death penalty debate in the U.S. Maybe Kirk was acting out a form of civil disobedience. The question is, if he had failed and been caught, would he have been willing to face the punishment on that planet for violating their laws?
Kirk was not in a position to engage in civil disobedience, because he was not a member of that culture. He was an outsider imposing his values without consulting anyone within the culture, without acknowledging any agency on their part or any right to choose for themselves. However well-intentioned it was, it was blatant cultural imperialism. It was the Capellans' place to defy the custom. It wasn't his place to force change upon them.
(Besides, civil disobedience entails unresistingly accepting the penalties for violating the law. Thoreau and Gandhi and King let themselves be arrested and tried when they defied immoral laws. Kirk and company ran for the hills and violently resisted capture.)
The problem I have is that the Prime Directive is completely amoral. To me, it's ridiculous to be relativistic to the point where everything is relative and every cultural practice or interpreation of truth or law deserves the same level of respect.
That's not what it's about. Look at British and American cultural imperialism. These societies went into other cultures with the best of intentions, with the belief that they were acting in the name of positive morals. But they ended up badly oppressing and damaging those cultures, because their own cultural biases blinded them to the fact that the solutions that worked for them wouldn't necessarily work for another culture, that some cultural differences are not
morally wrong but just different, and that even if there are genuine wrongs that need to be corrected in another culture, the people who are part of that culture and understand how it works are the ones who need to solve those problems. Outsiders who don't understand the culture may end up imposing solutions that do more harm than good. And change imposed from without can't really work; it only works if it comes from within.
So it's not about amorality. It's about recognizing that other people need to sort out their own problems, that you can't always fix things for them, and if you try, you can do more harm than good.
When I was in college, I had a friend who broke off contact with me because her boyfriend didn't want her having male friends. I recognized this as a warning sign of a possible abusive relationship, so I went to the campus women's center to ask for advice about how to deal with it. And what I learned from them is that there were limits on what I could do, what I should
do. Even if she was in an abusive relationship, I couldn't make her change. I couldn't impose a solution. Not only would it not work, but it would make me no better than the boyfriend, because I'd be trying to control her choices too. The only way her situation would get better was if she decided for herself to make it better. I could (and did) send her a letter expressing my concerns, send her brochures from the women's center, but otherwise the only viable, ethical solution was to respect her wishes and keep my distance, to give her the space to make her own decisions rather than trying to make decisions for her. It meant that things might never get better for her, but the reality of the situation was that it simply wasn't my problem to solve -- it was hers. (And I eventually heard from her again and learned that she'd left that boyfriend on her own, without my intervention.)
The Prime Directive is based on the same principle. Cultural imperialism is to nations what abusive relationships are to individuals. It's about thinking you're entitled to make decisions for someone else instead of respecting their right to make decisions for themselves. And it's never the right way to help them. If they have problems, they need to take responsibility for solving those problems themselves. If you try to fix things for them, to make them change the way you think they should, you'll probably just make things worse, and it's more about serving your own self-interest than respecting theirs. You can offer advice and support if
they're willing to seek it out, but the choice to act has to be theirs, because the responsibility for their fate is theirs.
Out of universe, I'm not sure why the Prime Directive was created for the show other than to be employed as a dramatic device within stories, and to also show that imperialsim didn't go out into space with mankind in a time period on Earth (the mid-1960s) when imperialism and self-determination were big geo-political buzz words.
I think the latter was the primary reason. It was TNG that turned it into more of a dramatic device. Particularly in "Pen Pals," which introduced the awful, nonsensical "Better to let them die than risk damaging them" interpretation. There's no way that makes any kind of moral statement about our world; it was introduced purely to create a philosophical challenge for the characters to wrestle with.