I'm certainly not singling out U.S., or Europe as "culpable offenders". The U.S. is my society, so I know it better and I feel its societal obligations more strongly. As you point out, the Western countries were simply the ones that got there first. And they are also the first to be figuring out how to fix the problems they've caused. Doesn't make them morally better or worse than countries that for historical reasons (smaller economies and lack of technology) have caused less environmental damage.

Also, given that you seem to already agree we have the obligation, your insistence on dis-acknowledging our cultural past as a source of the obligation seems odd. Nobody said the obligation had only a single source. The only reason to get angry, so far as I can see, is if a person thinks current steps are perhaps nice to do, but not obligatory. I fail to see how a "never-ending tower of recrimination and anger" can arise from someone simply giving an additional reason that supports the decision we've already made (that we have an obligation).