Amazon won't raise any monopoly red flags until it's responsible for the vast majority of our non-public infrastructure; it is simultaneously growing toward becoming both a horizontal and a vertical monopoly in every field it operates while not technically meeting the definition yet.
I think the issue is that many people see monopolies as a good thing, as long as they are not being very blatantly abusive (and especially if you can say, "well look, they only control 80+% of the market!"). Examples: Thiel, Friedman, maybe there are others.
The march towards efficiency, productivity, and profits naturally cuts into redundancy, diversity, and competition. Same goes for index funds, holding companies, etc.
I wonder if there is any way we can find a balance, because it seems like there are so many cases where giving up some efficiency/productivity for some other traits is desirable (renewable energy, research and development, health, safety, etc.)
One problem is the priorities of regulators. AIUI the US is concerned about direct consumer effects, whereas the EU is more concerned about whether competition is harmed. The problem is that consumer effects can be harder to spot, and if you have little competition, you perhaps don't know what you're missing.
