Archer and Phlox alone choose for this world.
They simply didn't commit their involvement beyond the point of no return. There's still plenty of time for a cure to be found by other parties, for other powers to intervene, for Earth's government to overrule Archer's decision of what sort of aid to provide, etc.
By easing their suffering, perhaps Archer even improves their chances of finding a cure on their own.
Had Archer given them the cure, that
would have been an irrevocable choice.
no, that's not what happened. A decision not to get involved would have meant not working on a cure at all and leaving the area. They WITHELD a cure that they already HAD-That's a decision by omission, no different than having a bottle full of water and denying it to a man dying of thirst on the street, or denying a life preserver that you're carrying to a drowning man in the waters below. And then Archer tried to rationalize denying a cure on the basis of picking a species that Phlox felt "deserved to live more" was somehow NOT playing God, when really his decision was the very definition of "playing God."