Also, Sisko said that the colonists in the DMZ "chose to live with the Cardassians", and he talked about "our"/the Cardassian "side of the DMZ".
Wouldn't that imply that the DMZ IS the territory with the planet in Journey's end and that the planets in question have a similar agreement? I think the writers of FTU definitely had that concept in mind.
"Journey's End" was very specific that Dorvan V would become a Cardassian world, without any sort of autonomy, and with Cardassian citizens forming 100% of the population - even if in this exceptional case, those citizens weren't biologically Cardassian, but human.
The DMZ worlds are very different beasts in that respect, definitely retaining their autonomy. However, it's perfectly possible that things were renegotiated after "Journey's End". After all, in that TNG episode, there was no talk about allowing any colonies to reside within the DMZ: the episode was solely about a simple border being drawn, and worlds on the wrong sides being evacuated. Perhaps the DMZ was invented as a compromise after "Journey's End" made things politically difficult?
Certainly there was never any suggestion that Cardassian law would be observed on Federation colonies or vice versa. The "sides of DMZ" thing seems to be limited to this exhance from "The Maquis":
Sisko: "I thought these colonists wanted to stay. That they refused to evacuate." (But apparently didn't want to make the Dorvan V concession of becoming Cardassians!)
Cal Hudson: "The treaty gave away their territory to the Cardassians, territory that these people had invested their lives in. Now, Ben, if you knew them as I do, you'd know why they can't leave. It's a bad treaty. The Federation gave away too much."
Sisko: "Several Cardassian colonies wanted to stay on the Federation side of the Zone too. It seemed like a reasonable compromise."
Now, Hudson says that "the treaty" gave away territory, while Sisko says "it" was a reasonable compromise. Perhaps we're seeing a development where "the treaty" is the one referred to in "Journey's End", without any DMZs, and "it" is the later compromise that gave birth to the DMZ and the autonomous colonies within.
If Sisko had bombarded the planet with instantly lethal toxins, there is no way for Sisko and crew to avoid big trouble.
I'd tend to side with the posters who feel starship captains have broad authority on this. Kirk was going to massacre a planetful of people in "Taste of Armageddon", too, and his crew seemed to concur. That the crew of Garth of Izar didn't concur, but sent their skipper to a mental asylum, probably speaks of different circumstances.
In "For the Uniform", there wasn't opposition from Dax, Kira, Worf or O'Brien, even though the four would represent four very different factions: Sisko's closest cohorts, outside observers with possible resistance fighter sympathies, extremely law-abiding busybodies, and average Joes with their heart in the right place. That more or less tells that Sisko's actions would have enjoyed wide support in Starfleet, too - perhaps wide enough that the letter of law would not have mattered.
Timo Saloniemi