If person A drives a truck, and person B writes code at their desk, it doesn't make sense to say we have to equalize their carbon usage, whether per person or per $ of income or output. Some activities inherently use more fossil fuels than others. Making them all use equal amounts is not a reasonable goal, just because we are trying to reduce them all.
Why not? You are assuming each country does basically the same stuff, rather than a divergent set of stuff they do best. If you drive people around in a car for a living, and I don't, it's palpably unfair to hold us to the same carbon budget. If you weren't driving me, I'd be driving you!
There is no reason the industry in one country should be exactly as carbon intensive as that in another, any more than the IT sector should be the same relative size, or the steelmaking sector should be the same.
