This argument cuts both ways. If Amazon isn't a moral entity, then there's also no moral violation if they screw you over.
Everything else is attempts to extrapolate from that.
Many things that are punished if an animal does to a human, are accepted by the billions if humans do to animals.
Many times an adult has a responsibilty a child does not.
The Amazon example is one of the latter kind.
Besides morality there are legal systems. As you get more and more kinds of things, it is expedient to represent corporations as legal entities, but often they are held to a higher standard than just random people. Since a corporation can employ many people and machines, to prepare every sale, they are held to a higher standard for transactions, taxes, reporting, quality of product delivered, and so on. They also have deeper pockets and can take the hit.
I don't see any reason why it should be ok for people to knowingly rip Amazon off. There are worse things (by far) that someone can do, but there's no real justification for doing it.
To compare a company's actions to those of a mosquito strikes me as quite silly. Amazon is run by people who make conscious choices and who are responsible for their actions.
I see this all the time on HN.
Companies don't "do things". The managers (and ultimately Bezos as the top manager) are the moral actors here. "Amazon" is just shortcut name for all the people that work there, this set is ever changing.
In that case, it's not a moral violation if they screw you over, but it's not a moral violation if you end them for screwing you over either. The mosquito isn't violating morals when it bites me, but I'd still have no problem eliminating them all from my backyard if i could do it in a reasonable manner. Not many people claim it is immoral for me to swat the mosquito.
I just don't see why that kind of nihilism suddenly becomes more plausible than usual when you're buying something from Amazon.