Just as Luffy’s aspiration is easily misunderstood by others in the manga, it is initially misunderstood by the onscreen audience too. He wants to be the king of the pirates, yet he does not want to be the most tyrannical of tyrants. He defines pirates’ vocation differently, to not be about looting and killing, but seeking of treasure and adventure with freedom. (But what if the treasure found is from looting? Will it be returned or shared?)
Thus, Luffy is unlike the typical pirate. He is cheery not grumpy, loyal not dishonourable, infectious with enthusiasm not disdained or irritating… Even though he seems largely happy-go-lucky, which would make him unhappy-go-unlucky too, he is actually focused and resilient, both mentally and physically (if you know what I mean, with his rubbery powers). Most importantly, he is righteous, not self-righteous.
His friend Koby has a more typical and straightforward aspiration – to be a marine who upholds law and justice on the seas. However, he makes the mistake of idealising the job. It turns out that high office-holders among the marines are kind of pirates in uniform, in cahoots with actual pirates. While Luffy always seems curious but clear-minded, Koby is usually featured obedient yet confused, unable to resolve the unfortunate paradox by thinking out of the (proverbial labelled) box.
Here we have Luffy who wants to be the best pirate, who does not engage in piracy, versus Koby who wants to be a good marine, who is subordinate to evil superiors. But is Luffy not like an incorruptible marine without uniform, while Koby sort of working in proxy for the very pirates to be arrested? Luffy naturally gets unfairly demonised by the marines with his unconventional heroic ways, becoming a wanted ‘pirate’ with the highest bounty ever. He must be doing something very right then!
Maybe, Luffy should redefine himself as a pirate hunter instead of a pirate, or a treasure hunter since finding treasure is his real goal. (But where is the fun in that?) What is the treasure really anyway? Even before finding it, are not the lessons learnt and friends made along the way already many precious gems, treasured experiences to be enjoyed? Why must the treasure be right at the end, as ‘one piece’ only?