Consumerism is a cultural problem, not a supply chain issue.

It is both. Capitalism encourages supply chains to be formed based purely on metrics such as cost on the production side. Nothing is planned further than what will minimize the cost to the company, so that profit is maximized. While roughly the same amount of consumption is done by the working class in its consumptive capacity, this does lead to greater consumption and waste by corporations as part of the production process. When we take control of our workplaces, we will be much better able to account for and make rational decisions regarding such externalities.

And to some degree, it's also pointless to try to separate "culture" from "economics". They influence each other. People don't consume simply to consume, but because of the pressures put on us by the system. We drive not just to drive, but because we need to get to work and school, and because capitalists have destroyed our public transportation options. The reverse—our affect on the system of capitalism—is much less powerful these days, as we've allowed ourselves to become powerless and subjugated ourselves more and more to the class war. Certainly cultural elements will be necessary to overcome this, like building a culture of loyalty to one's fellow workers and the unions which empower us, and eschewing advertising's daily effects on our habits. But to imply it is "just cultural" is missing a lot.