We've already passed the tipping point where there's enough carbon dioxide (and other green house gasses) in the atmosphere that sea levels are going to continue to rise irregardless of what we do to curb carbon emissions. So while we many not be able to stop that, we can still cut down on diseases caused by air pollution including asthma, bronchitis, lung cancer, and brain developmental diseases. The other argument is that even if we stop polluting ourselves, China will still be burning so much coal that the pollution will spread to us anyway (the smog above Los Angeles originates mostly from China and they are carried by winds over to the U.S. and other parts of the world).