on David Bentley Hart's "Mammon Ascendant"

Others like Acton's Samuel Gregg have written longer and more-sustained critiques of Hart's FT article (or more broadly, his claims in this area), so I don't want to re-create that wheel, but I do have a few thoughts/comments.

For one thing, Hart only does a decent job of explaining the title of his article (Mammon Ascendant) and does little or nothing on his subtitle (Why global capitalism is inimical to Christianity). But I want to focus on a few passages...

As late modern persons, we live in a society whose highest values—in every sphere: moral, religious, economic, domestic, cultural, and so on—can loosely be described as “libertarian.” We understand freedom principally as an ­individual’s sovereign liberty of deliberative and acquisitive choice, and we understand individual desires (so long as they fall within certain minimal legal constraints) either as rights or at least as protected by rights. And we are increasingly disposed to see almost every restriction placed upon the pursuit of those desires as an unreasonable imposition. Our natural economic philosophy, then, is of course “neoliberal” (or, as it is also called in America, “neoconservative”) while our natural moral philosophy is voluntarist, individualist, and hedonist (in a not necessarily opprobrious sense). Not only is there no contradiction here; there is an essential unity.  
 
This may be correct-- first, a broadbrush description of our approach to our own lives, but second, assuming that we're talking about life outside of political beliefs and actions. 

On the first: it's not clear how much this has changed over time. (I think there's been a significant change in this regard, but Hart does not make the case here-- and in any case, it's more complicated than he allows.) As a decision-maker, I see my actions as they impact me, which includes how it impacts those in my circles. (The extent to which the community fits into "my utility function" may have changed over time, but that's complicated too.) As such, Hart is correct in a manner that is relatively uninteresting: we are (and have been) voluntarist, individualist, and "hedonistic". (Following Hart, I'm using this latter term in its non-pejorative sense; see: Piper's "Desiring God" and a more favorable interpretation of Joel Osteen's outlook on life.)

In terms of politics, his summary does not hold. Americans generally hold political views that want freedom for themselves, but not so much for others. Some of this is paternalism-- not trusting others' decisions and wanting the government's assistance in these matters. (We never want the govt to paternalistic toward ourselves!) Or we want the government to do something that "the market" won't do well enough for our tastes-- e.g., redistribution to the poor/needy. Some of this is envy: wealth should be redistributed from "the wealthy" (people who have more than me) to me and people like me-- either "the [more truly] needy" or at least, "the relatively needy" (various schemes to redistribute to the middle class). But a lot of it is "rational ignorance and apathy"-- that government does all kinds of stuff and we're not paying much attention, so we go along for the ride. All of this runs counter to Hart's claim, if he intends the claim to extend to our (decidedly non-libertarian) political lives.

Mind you, part of the difficulty of convincing American Christians of this lies in the generous vagueness with which we have come to use the word “capitalism” in recent decades. For many, the term means nothing more than a free market in goods, or the right to produce and trade, or buying and selling as such.

Agreed. But this is not simply a problem for Christians. The term is used to mean all sorts of things!

Hart moves to define capitalism and place it within the 19th century: "...we can say it is the set of economic conventions that succeeded those of the “mercantilism” of the previous era, with its tariff regimes and nationalist policies of trade regulation, and that took shape in the age of industrialization."

A few thoughts here: The extent to which mercantilism was dispatched is exaggerated here. And mercantilism (or close cousins of it) are still one of the dominant players in our political economy, combined with its connections to cronyism and interest group activity. Moreover, if there's been a reduction in our penchant for mercantilism, it's far safer to put that at the feet of the necessities of global competition, rather than some philosophical change about political economy. 

Hart then says of capitalism: "It generates immense returns for the few, which sometimes redound to the benefit of the many, but which often do not..."

This is Trumperian balderdash, misunderstanding an opening principle of Econ 101: mutually beneficial trade. 

Toward the end, Hart moves into biblical support for his position, making a common set of exegetical mistakes and confusing "biblical socialism" with socialism as a system of political economy.