The obvious argument is the adage that "If a company's only goal is to grow at any cost it is not a company. It's a cancer."
Secondary item is that a company of this scale has the ends and means to ward off any competitor and eventually set the wages for an industry. Companies scaling to this size is evidence that the taxation system is too lax and allows money to be funneled out of the loop.
Think of it like a pool pump that has sprung a leak. It keeps sucking in but not pupping out into the pool, Amazon is amassing this money by NOT spending it on the economy. Eventually your pool will be stuck at the lowest line of the pump inlet.
> Amazon is amassing this money by NOT spending it on the economy.
Quite incorrect on this point, Amazon has pretty small cash reserves compared to peer tech companies. Even then, if Amazon were merely putting that money in the bank, where is it going? It's getting loaned out to other companies and consumers, who are spending it, investing it, etc via fractional reserve banking.
Because we get more than we had before. As costs go down, the risk of innovation goes down, we're able to be more responsive, able to do new things. People are able to have more variety to meet their individual needs and preferences.
In short we get more or work less and the overall quality of life for everyone increases.
It's very hard for a corporation to get large without explicit or implicit government support. Truly competitive markets do not allow monopolies to develop in the long-term.
Ok, I'll bite. Why? It's not like there's some natural law against it, so you need to provide an argument for why you think they shouldn't.