Aren't people who prefer to give Rupert Murdoch the benefit of the doubt adorably trusting? At the precise moment his Fox News appears to have finally abandoned even the quarter-arsed pretence of impartiality, allowing Tea Party-backed candidates to fundraise on air in return for exclusive, uncritical access, there are those on these shores opining that Murdoch winning full control of BSkyB really is no biggie.

Well, quite. What's the worst that can happen?

Even as Sarah Palin appears to be fashioning a run at the presidency without appearing on any media outlet other than the one that pays her (she has her own show on Fox), there are those wittering that Murdoch basically already runs Sky, so gaining full control won't alter the UK's media landscape.

Were things across the Atlantic not looking so mind-boggling, you could almost envy that cosy, antiquated assumption that the "media landscape" is something settled, as opposed to in a state of historic flux. Sarah Palin's tweets may have to be ghostwritten – I know, even Darren Bent can fart out his own – yet, as Time magazine observed this week, a single one of them can dominate a news cycle, while one of her speeches can monopolise three news cycles.

The fact that Palin is the figurehead of a movement most of whose emergent stars would appear to be better suited to prison or lunatic asylums makes it hard to get one's head around quite what is happening to mainstream politics in the US at the moment. But for people who'd ideally like prospective leaders of the free world to be able to point to China on a map – and not to claim that they'd have told the Nazis Anne Frank was hiding in their attic because lying is always wrong in God's eyes – it doesn't feel madly encouraging. When candidates for public office are being promoted by Fox on the apparent understanding that they will appear exclusively on Fox, classing the network a fascist broadcaster seems less and less hysterical.

Indeed, things have come to such a pretty pass that earlier this year even Matthew Freud, Murdoch's son-in-law, felt moved to tell a reporter he was "ashamed and sickened" by Fox News. Poor dear. Yet while Matthew might be a useful valet when Rupert wants someone to organise a private jet to spirit David Cameron to his holiday yacht for drinks, his views on this ever-more powerful force in US politics are of as much concern to Murdoch as those of Kerry Katona. Indeed, only a couple of months previously Rupert had gone on the record to defend Glenn Beck's comments that Barack Obama is a racist, declaring: "He was right."

Happily, the real players in the family are able to see the bigger picture, which is why James Murdoch last year described the BBC's activities and ambitions as "chilling" – high praise indeed from a chap whose dad owns 40% of the UK newspaper market and enjoys a satellite monopoly gifted to him by an obsequious Margaret Thatcher.

Happier still, that obsequiousness endures. Within days of the coalition government being formed, it emerged that one of the prime minister's first meetings was with the News Corp overlord himself. According to one account, Murdoch was "ushered up the back stairs of Downing Street" – which sounds like both a statement of fact and a euphemism for what Rupert has been doing to successive governments for decades.

Yet still there are those who regard this abusive relationship as totally normal. Arguably their most baffling cry is that Murdoch "isn't political" because he has supported both Tory and Labour in the past, a piece of spectacularly muddled thinking summed up this week by one commentator who reckoned the BSkyB deal should go through because "Murdoch has no real politics beyond what's good for Murdoch".

It is a mark of how deeply some have drunk from the Kool-Aid that Rupert-über-alles doesn't count as a political position – when history, and many a weighty political memoir, shows it has meant the only policies recent UK governments can feel comfortable implementing are those that suit Murdoch's business agenda. From Thatcher through Blair to Cameron, our democratically elected leaders have tugged their forelocks to an unelected foreign tax exile in gibbering fear of losing his papers' support, allowing Murdoch to regard a change of government as the mere shuffling of junior personnel.

Currently serving as his host organism is David Cameron, who clearly has no intention of resisting, which means it's down to Vince Cable. If his speech this week meant anything, the business secretary must block the deal to protect the media plurality essential to democracy.

Writing last Sunday in support of such a block, David Puttnam revived a warning of Lord McNally's from only a few years ago. "In the 1930s," his lordship had reminded parliament, "we were afraid that the fascists would take over the government and then control the press; in the 21st century, there may be a danger that the fascists will take control of the press and then control the government. The dangers are there."

Indeed they are, as an increasingly rampant Fox News foreshadows.

marina.hyde@theguardian.com