> Just don't understand how one could be convinced these days of the fundamental conceit that even a properly profitable company is necessarily going to provide good things for people downstream, or for society in general. 

if one has worked in a number of business it should become fairly obvious that good products and good revenue are orthogonal phenomena (sometimes they align of course)

  > What is the argument for that in general again?

i think the general conceit is that bad or good product, someone is paying and they are getting some kind of value so who is anyone to say its good or bad for society?

  > the idea that companies with a self interest in profit will reliably help people or the world

wasn't this idea put forth strongly by milton freidman and the chicago school - "greed is good" [1] - because more economic activity rises all...? i have to admit intuitively it sounds good even if its probably b.s [2]

  > It just does not at all feel rational, its like everyone in the world is dreaming.

well, at least some economists anyways....

[1] https://www.youtube.com/watch?v=RWsx1X8PV_A

[2] https://www.nytimes.com/2020/09/13/business/dealbook/milton-...