Protecting water quality is what I do for a living.
My point was water pollution in India and China don't flow uphill and contaminate our water supply. The hydrosphere is very fragile, but impacts tend to be more localized to specific watersheds simply b/c unlike air, water can't travel uphill. The dead zone in the Gulf is a result of fertilizer runoff from us, not from impacts across the world.
But I'm glad you brought up the dead zone in the Gulf...the main problem is agriculture is exempt from the Clean Water Act. Therefore (much like global warming) there is currently no regulatory mechanism to stop it.
I agree that it should be addressed, and I wish it got more media attention.
But protecting the gulf doesn't preclude CO2 regulations.