impartial journalism is entirely possible.
It's certainly possible, but if you can actually show me an instance of it, I'd be quite surprised. I don't recall seeing such a thing. Ever.
There's selection bias, where the story that is told is not the only story, and/or leaves out pertinent details that variously pollute the information transfer to the information consumer. This occurs at the publisher, editorial, reporter and information source levels.
There are errors in collecting information, which can be characterized as "impartial but wrong" which entirely undermines the value of "impartial."
There's the social underpinning, such as the assumptions by the platform from publisher down to reporter buy into memes like the drug war, human trafficking, mommyism, military adventurism, etc. as right and proper undertakings and tell stories in the context of the presumptive matrix that results from those memes.
There's ad-pumping, where the advertising pays more money in when more eyes are attracted, which creates a loop based on popularity rather than accuracy.
There's comment "moderation", where "I disagree / am offended / am trolling" can strongly affect visibility of information -- depending on the site, that can come from privileged (and usually wholly unqualified) individuals, as here on slashdot, or from the crowd, as on reddit.
It all adds up to an extremely formidable gauntlet that information has to run in order to get from wherever it arises over to the consideration of the consumer.
And, not that it's part of the problem of actually achieving impartial journalism, but were you to completely get past every aspect of that somehow, then you still have to find an impartial audience or all that work is for nothing.
IOW, if you manage to present the facts, all the facts, nothing but the facts, and your audience cries "fake news" or drags prejudice, superstition, confirmation bias, or anything from a very long list of similar cognitive failure modes into it, well, there you go. You might as well have written an SF novel.