Flooding a market with below-cost goods (or "discounts"), to drive out competitors so that you can generate a monopoly, is predatory pricing -- literally by textbook definition. It's also illegal, it is a direct violation of US federal anti-trust law.
https://www.ftc.gov/tips-advice/competition-guidance/guide-a...
No one is against "discounting" (as in, coupons for Cheerios, or discounts for bulk orders). But illegal predatory pricing is often passed through the economy under the disguise of "a discount", and it's correct for people to challenge that.
