Opium does not save lives, it's a painkiller. And it is not the same at all. If millions would die if people stopped selling medical opium, I am sure you would argue it unethical to stop production of it before there was anything to replace it.

I would say a better analogy is selling alcohol to an alcoholic because you can't just cut off the supply right away because they could die from the abstinence symptoms. You need to get them off their dependency slowly. In this case, you need to decrease their dependency on oil and gas slowly and replace it with clean alternatives, which are currently way too expensive for the developing world.

Countries would literally go to war tomorrow if they lost their supply of oil and gas.