...except that you can refuse to do business with them and they're not going to kneecap you or burn down your business
I'm not among those complainers, having grown up in a small town where you couldn't get anything without mail-ordering it until Wal-Mart came in. But I could certainly be swayed to their point of view if Wal-Mart starts selling counterfeit or extremely low-grade crap like the rope ericbarrett purchased.
I don't; Walmart courts brands, tempting them with access to thousands and thousands of stores. As soon as an irreplaceable proportion of the brand's revenue comes from Walmart, they start turning the screws, lowering the price they sell the product at, forcing the supplier to reduce costs. This often ends up with the brand producing a different product, with the same name, to sell at Walmart.
I can't find fault in any party's decisions in these scenarios; consolidation is the inevitable result of capitalism.
https://www.fastcompany.com/54763/man-who-said-no-wal-mart is one example of a company that saw what was coming and refused to go along with it.
Amazon is starting to get worse as of late, but it still has the most reliable online delivery so far.