"Capitalism is when Walmart offers a discount on Pepsi, at razor-thin margins, and somehow this is maximally extracting from the middle and lower classes"

Pepsi is exchanging profit for market-share. Be serious. Everyone else is just charging the standard price.

Market failures ought to be accounted for with regulation (they often are, that's what Liberalism is for), but this is not one.

The unessential garbage fuelling our obesity crisis has no place in the conversation about the affordability crisis whilst policy-makers and armchair experts are mulling a sugar tax, which would just raise the price. Notwithstanding, profit margins at grocery stores are not large in the first place. The reason profits are breaking records is that population is also breaking records, and customers are spending more on boutique animal alternative or organic boxed products. Margins on produce are as thin as ever. Canned black beans and soup are not making their billions.

Did you forget about the "creative" methods that Pepsi used to (illegally) ensure other retailers could not offer low margins on Pepsi?