This is a great "anecdote" (I don't have a better word...). It's easy to imagine someone finding cheap goods, setting himself up with fulfillment by amazon, and setting a price, and then Amazon deciding his price is wrong, buying his stuff, and relisting it (after all, it's already catalogued in their warehouse) themselves.
I don't think anyone thinks such behavior would be morally alarming... but that's certainly a common perspective when it comes to high-frequency stock trading. What makes the difference?
1. Normal people don't have access to HFT equipment, giving a handful of corporations an edge over the rest of us.
2. Most people really don't understand HFT.
I think #2 is actually the real reason people are up in arms about HFT, honestly. It's new, scary, and allows corporations to extract money seemingly from nowhere.
I think the "extract money seemingly from nowhere" might be the operative part here - one thing that almost everyone shares is an instinctive understanding that money does not come from nowhere. In the absence of further information, many will be suspicious that it's probably coming from themselves.
I'm with you on the reasoning, but I hate the logic of
1. I don't understand phenomenon X
Therefore,
2. Phenomenon X must be stopped
To your point #1 in particular, it's true that normal people don't have access to HFT equipment, but they also don't own warehouses full of third-party goods (and would find those probably more difficult to obtain), so it's hard to explain in those terms why Amazon's hypothetical maneuver is different from HFT.
I doubt the seller would mind. Amazon could have not bought it and let the seller hold onto the inventory longer. Amazon buying it from the seller brings the seller profit from future to now.
I don't think anyone thinks such behavior would be morally alarming... but that's certainly a common perspective when it comes to high-frequency stock trading. What makes the difference?