Either way, only what developed countries (and China, India, Brazil, maybe Nigeria and Indonesia) do today matters in the fight against climate change. There's no one else to point fingers at, unless you're looking for an excuse to do nothing.
As a percentage of total population, the number of people who emigrate from a poor country like Niger to a developed country is quite small. And they'd likely be poor there too, and consume fewer resources on average.
I think "doing nothing" is what people who advocate reduction of consumption and having fewer kids are doing. Those plans won't be implemented and they won't work. What I'm advocating is technological development to solve the problems related to global warming.
You may think so but that's not the case. I don't know of too many vegan-organic-bike-riding-hippy types who think we shouldn't invest in grid-scale storage, renewable power, carbon capture, or more efficient heating & cooling, manufacturing, or transportation systems. Arguably the only tech many of them oppose is nuclear power.
(Voluntary) reduction of consumption has the side-effect that the electorate becomes more agreeable to measures such as carbon taxes. An SUV and burger-loving electorate will never vote for them, because they would make SUVs and burgers more expensive. Without carbon taxes, there's no market mechanism to control emissions. And there's less funding for technological development or subsidies to green tech.