We see an example of karma in this episode when Gin does not want to kill Sanji because Sanji fed him when Gin was on the brink of starvation. Having experienced the same thing himself, Sanji makes a point to feed anyone who enters the restaurant, no matter what, and here he is repaid for that by Gin’s sense of honor. It is pretty clear that Gin is not a “good guy” but a violent pirate, yet he still follows his own personal code, which is relatable to many people; very few humans are truly good or bad but instead live in shades of grey, choosing their actions based on their own interpretation of morality. Gin even encourages Don Krieg to kill him for disobeying his orders, stating that he would do the same thing if he were in Don Krieg’s position, demonstrating that he is steadfast in his decision to spare Sanji, regardless of the consequences.
Luffy wanting to destroy the boat so that no one has it is reminiscent of King Solomon splitting a baby in half in a popular Bible story, the idea being that if no one can win, the conflict is over. We also see Sanji willing to die to protect Zeff as another point of honor. In both of these cases, it seems there is an overarching goal to follow their own personal codes of conduct regardless of how it affects other people, which directly contrasts the example of Gin. Gin is making a choice that ultimately will only harm him, but Luffy would harm the entire restaurant staff by destroying the boat, and Sanji would harm Zeff by failing to deliver on his dream to seek the All Blue. In a certain sense, then, Gin is actually the more honorable one in this episode, which likely speaks to their differences in experience: Gin has been a pirate leader for a long time, while Luffy is practically brand new to the sea and Sanji has likely not spent much time outside of Baratie.
Don Krieg’s suit of armor has significantly better technology than a lot of what we have seen on the show thus far, and I imagine that this is a large part of why he was able to conquer so much of the East Blue. In any war or battle, the side with the superior weapons is typically going to be the victor outside of rare edge cases with prolonged guerilla warfare and the like. With defensive capabilities as well as offensive weapons for short-range, long-range, single-target, & area-of-effect attacks, it makes sense that not only would he make short work of most of the sailors we have seen, that many of them would be quick to surrender and join his fleet in the face of an unbalanced fight.
Last note, this was the first time I noticed in the opening animation that Gold Roger had been captured & sentenced to death. I suppose I presumed that he was making some sort of announcement to the world before just going into hiding, or maybe he was old & sick and preparing for death, or he was just a legend, a myth, a rumour altogether, but he was apparently caught by the Marines (or a similar group) and given a public execution, during which he stated his challenge for people to find his treasure to the large crowd that had gathered. This could still be just a story or something, but it does lend more credit to the overall narrative.