That argument that GP is making isn't that low prices are bad for consumers.
The argument is that amortized over the lifetime of the business, the prices are actually significantly higher because they are able to momentarily drive their prices down, eat the losses long enough to run their competition out of business, and then immediately break the low-priced agreements with their customers.
Sure, they may be a commodity product now. That shouldn't exempt them from holding up their agreements from when they were still competing for market space.