I wouldn't consider it harmful interference with their society if I did everything according to their native laws and traditions.
If you were wearing a Military Uniform of your own nation and as a part of a Crew whose mission was to in effect be a representative to their country?
As far as being a Starfleet officer at the time, IIRC (and it's been a while) he offered to resign his commission AND was reprimanded for his actions.
So in effect the immigrant soldier who beats someone should be given a talking to? Wow I would love to servie in that military, blow a few people up and you get rations instead of Mess Hall food.
Its the same thing, Worf did interfere, unless you are honestly suggesting that he did not for a single second consider the ramifications of his actions. Once again in the end I am forced to point out he is not just a Klingon but a Starfleet Officer who has to answer to their rules and laws, he choose that life, he did not have it forced upon himself. Instead of killing Duras he could have collected evidence, laid charges and tried to get to either extradited or punished within the Empire.
As to his resignation, he didn't resign before he killed him, but after. All that means is that it is easier to get forgiveness then it is to get permission. It could also be taken as a cowardly act to try and avoid the punishment he knows is due him.
The fact is there was no investigation afterward into what happened, Picard was once again allowed to dispense summary justice, no appeals afterwards, no professional examination, no thought on the consequences of their actions, just merrily along to the next adventure.
There may be times when we are powerless to prevent injustice, but there must never be a time when we fail to protest.
-Elie Wiesel
Dreaming in Color Living in Black and White, Sitting in a Grey Day Leaning on a Bright New Tomorrow.
-Billy Ray Cyrus