It is true that they disagree. It is not true that they're lives are definitely harder. For every person in the US, there are four in China. Even imagining that China had the same wealth distribution as the US, which it does not, that still means there are vastly, vastly (at least 4x) more people with lives that are empirically more painful, with less medicine, less availability of electricity, and less food. This isn't because China is doing a bad job, it's because there are a lot of people.
You are correct that there are many more people in China and that being poor in China is worse then being poor in America, but the solution is not to export global competitiveness to other countries until their quality of living is on par with Americans. Once that ability goes away it will not come back, and as you can tell no one really cares about the plight of rural Americans who stand to be the biggest losers from the change
No one is talking about giving developing countries a pass until their GDP per capitas are on par with developed nations..
Even with business as usual emissions, China's per capita GDP will maybe be half of what the US's will be in 35 years. I doubt climate mitigation policies would chip away at much of that difference.
