It's not illegal to drive down prices in a competitive environment. In fact, economic theory says that in a sector that has 'perfect' competition, prices will essentially be the cost of production. What Amazon is currently doing isn't illegal. In the future, if they abuse their dominant position to jack up prices, they might be in some trouble. But running on thin margins isn't illegal, and it seems Amazon has create…
[1] https://en.wikipedia.org/wiki/Loss_leader
[2] https://en.wikipedia.org/wiki/Predatory_pricing
[3] https://en.wikipedia.org/wiki/Dumping_(pricing_policy) Dumping is a particularly interesting instance since there isn't a direct realized economic gain.