I've never been to Vietnam and I wasn't attempting to describe any specific people. I was just addressing the idea that being poor is not a condition that might raise the bar for disposing of one's trash "properly" (or, for that matter, doing almost anything else). Where I live I spend $52 a month to have my trash picked up (and it just went up to $54). I can totally imagine a person or family who can afford to buy some things made of plastic (pretty much one of the cheapest materials in the world) but who would still be strained by an extra $50 obligation. Or people who can afford plastic but still live in a community that cannot afford to offer this service. I've seen photos of people living in mud and straw huts without windows or running water wearing Nikes so I suspect access to industrialized waste might be more accessible than you think.

And I'm not saying even the poorest individual can't handle their own waste, I'm just positing that the effort required to do so is inversely correlated with income.

If anything I'd prefer if people were more careless with their trash in the "nice" places since this is where most of the people responsible for designing and producing this stuff tend to live and under our current arrangement these minds are somewhat insulated from the actual impact of producing long-lived objects of marginal utility.