Does corporate ownership of a newspaper compromise its journalistic output? Is independent journalism of greater public value? Is an "activist" journalist less relevant than an "objective" journalist? Can journalism be "objective" or impartial or neutral? If not, is it better to be openly partisan and/or "adversarial"?

These questions, asked by journalists and their critics down the years (not least by Noam Chomsky and Ed Herman), are being explored again in the light of Glenn Greenwald's decision to join a new independent journalistic venture financed by eBay founder Pierre Omidyar.

It followed his rise to prominence as the Guardian reporter who reported Edward Snowden's revelations about surveillance by America's National Security Agency (NSA).

Greenwald's championing of adversarial journalism is based on his belief that it can hold "the most powerful factions accountable, fearlessly, and without regard to threats or repercussions from the government or corporate factions."

He made that point in an interview with Amy Goodman, on Democracy Now! and expanded on it in an online exchange with Bill Keller, the former New York Times executive editor who is now a columnist with the paper.

Keller opens by defending "impartial reporting" as practised by mainstream news organisations, arguing that "journalists in this tradition have plenty of opinions, but by setting them aside to follow the facts … they can often produce results that are more substantial and more credible."

Greenwald concedes that the "standard model" for a reporter does not preclude good journalism. But it has "also produced lots of atrocious journalism and some toxic habits that are weakening the profession." He continues:

"A journalist who is petrified of appearing to express any opinions will often steer clear of declarative sentences about what is true, opting instead for a cowardly and unhelpful 'here's-what-both-sides-say-and-I-won't-resolve-the-conflicts' formulation. That rewards dishonesty on the part of political and corporate officials who know they can rely on 'objective' reporters to amplify their falsehoods without challenge Worse still, this suffocating constraint on how reporters are permitted to express themselves produces a self-neutering form of journalism that becomes as ineffectual as it is boring ... Worst of all, this model rests on a false conceit. Human beings are not objectivity-driven machines. We all intrinsically perceive and process the world through subjective prisms. What is the value in pretending otherwise?"

Greenwald contends that "honestly disclosing rather than hiding one's subjective values makes for more honest and trustworthy journalism. But no journalism – from the most stylistically 'objective' to the most brazenly opinionated – has any real value unless it is grounded in facts, evidence, and verifiable data."

Keller responds by pointing that mainstream reporters, "as an occupational discipline", suspend their opinions and let "the evidence speak for itself." And this is not simply an "individual exercise, but an institutional discipline, with editors who are tasked to challenge writers if they have given short shrift to contrary facts or arguments readers might want to know."

Keller believes that "once you have publicly declared your 'subjective assumptions and political values,' it's human nature to want to defend them, and it becomes tempting to omit or minimise facts, or frame the argument, in ways that support your declared viewpoint."

Greenwald hits back with a rhetorical question: "Why would reporters who hide their opinions be less tempted by human nature to manipulate their reporting than those who are honest about their opinions?"

As a case in point he mentions "the collapse of media credibility" that stemmed "from things like helping the US government disseminate falsehoods that led to the Iraq war and, more generally, a glaring subservience to political power."

He argues that the mindset if mainstream reporters "is nationalistic, subjective and activist … all journalism is subjective and a form of activism even if an attempt is made to pretend that this isn't so."

Keller is angered by the claim:

"'Nationalistic,' your word for the 'mindset' of the American press, is a label that carries some nasty freight. It is the dark side of the (equally facile) 'patriotic'. It suggests blind allegiance and chauvinism. I assume you do not use it casually. And I can't casually let it stand. The New York Times is global in its news-gathering … in its staffing (for starters, our chief executive is British) and especially in its audience. But it is, from its roots, an American enterprise. That identity comes with benefits and obligations. The benefits include a constitution and culture that, compared with most of the world, favour press freedom. (That is why your editors at The Guardian have more than once sought us as partners in sensitive journalistic ventures – seeking shelter under our first amendment from Britain's official secrets act). The obligations include, above all, holding the government accountable when it violates our laws, betrays our values, or fails to live up to its responsibilities … Like any endeavour run by human beings, ours is imperfect, and sometimes we disappoint. Critics on the left, including you, were indignant to learn that we held the NSA eavesdropping story for more than a year, until I was satisfied that the public interest outweighed any potential damage to national security. Critics on the right were even more furious when, in 2005, we published. Honourable people may disagree with such decisions, to publish or not to publish. But those judgments were the result of long, hard and independent calculation, a weighing of risks and responsibilities, not 'fealty to the US government.'"

There is more, much more, to the exchange, which gets extremely testy at times, and is always readable (click on the torture comments for instance). But, essentially, Keller and Greenwald repeat the arguments between a journalism that is "objective, neutral, impartial" and one that is "subjective, activist, adversarial".

Andrew Sullivan, in an excellent commentary on the exchange, sees virtue in both kinds of journalism. "I think readers deserve both," he writes.

But, he declares, "on the basis of this exchange, I think Glenn has the advantage. And that's because his idea of journalism is inherently more honest – declaring your biases is always more transparent than concealing them." He continues:

"That's why, I think, the web has rewarded individual stars who report and write but make no bones about where they are coming from. In the end, they seem more reliable and accountable because of their biases than institutions pretending to be above it all. In the NYT, the hidden biases are pretty obvious: an embedded liberal mindset in choosing what to cover, and how; and a self-understanding as a responsible and deeply connected institution in an American system of governance. These things sometimes coexist easily – as a liberal paper covering the Obama administration, for example, with sympathetic toughness. And sometimes, they don't – as a liberal paper covering the Bush administration, for example, and becoming implicit with its newspeak."

Sullivan concludes: "We need him [Glenn]. And with any luck, the competition will sharpen the NYT as well … It will only do better with Glenn nipping at their heels."