Get your logic straight - it makes no sense to bring up problems concerning global coordination to reduce greenhouse gas emissions, as though they are some sort of condition on your acceptance of the fundamental science.
Your assessment of the cause of the problem should be independent of your analysis of the solutions. If you don't agree with this I think you're a fundamentally dishonest person.
As for blaming poor brown countries: Taking strong action for them may mean people starving and rioting (note Equador recently): real societal pain. It's laughable to expect that of them before richer nations have really made strong commitments, commitments that don't necessitate severe social hardship. Once wealthy countries get their shit together, they can pressure/encourage the others to tow the line as a united front.
As for blaming poor brown countries
I'm sorry, it's just the entire "plastic in the ocean" is their doing. 90% or more of all plastic in the ocean comes from Asian and African rivers. We can't have straws here in california, but we barely rank in the actual pollution by pound in the ocean. I'm all for more biodegradable plastics to be used in single use items, but just the US, or the entire west, is not in any means the major culprit here
Look, plastic in the oceans is a bit of a peripheral issue.
The US takes the blame for a huge chunk of emissions historically. Passing the buck to other countries is the small-minded, easy thing to do. It's just as easy for someone in India or China to point the finger at the US or the west, or argue that their own contributions are insignificant.
If you have such a high opinion of the west, perhaps you should make sure the US is taking the moral high ground and leading by example. (It's not.)
I could buy that argument, but what can we do about the extreme pollution being caused in SE Asia by dictatorial regimes? We barely scratch the surface when it comes to pollution coming from China and India. Everyone loses their shit when and negative action is taken towards China, taking action to get them to reduce emissions will be very painful