>If the price stays low and never goes to high monopoly prices then it is a good thing.

Not necessarily, but it goes a long way to balancing out the negative consequences. The problem, though, is they've never had prices stay low. Eventually, prices go up. So far, Amazon does this through loss-leaders; products that have low prices allowing them to capture a market and charge high prices for other products as a monopoly.

>If a company becomes a "monopoly" by being cheap, and staying cheap, thats just competition by definition.

If that was all they were doing it would be legal.

Selling things at a loss doesn’t mean things are cheap it just means the real costs are being subsidized elsewhere.