Well, Olen is right, but I think she and MMM are writing from very different angles. Olen is writing about society, not the individual. She means that consumerism isn't the cause of systematic dysfunction. E.g., consumerism isn't the reason we have a whole class of working poor.
MMM writes about and to the individual, particularly individuals with a decent income (not the working poor). So, he IS right that consumerism is a problem for a family making $100k and saving nothing because they're trying to buy their way to prestige.
My guess is that Olen is targeting him because he's a rich dude who insists that his methods work no matter your income. Most folks who are actually poor or who study poverty or who have any real awareness of the machinations of poverty disagree with him on that one.