When you sup with the devil bring a long spoon, says an old proverb. And British politicians learnt last week that their spoon was too short when they supped with Rupert Murdoch. Irish politicians, please note.
Party leaders in England and Scotland have wanted to be friends with Murdoch because of his influence. Just as leading politicians here have been happy to rub shoulders with Tony O'Reilly, Denis O'Brien and others.
Murdoch denies that his media empire has the kind of power to influence public opinion that critics fear it has. But he does not deny that he uses his media to air his views. He told the Leveson inquiry in London last week: "If any politician wanted my opinions on major matters, they only had to read the editorials in the Sun."
The influence of rich media shareholders is also an issue in Ireland, as billionaire Denis O'Brien and the wealthy O'Reilly family tussle for control at Independent News & Media. Governments, too, have influence over the media by their power to fund State broadcasters such as RTE, turning on or off the tap of finance depending on circumstances.
Those who fund or control media are tempted to use their power to protect their own interests. Some local newspapers in Ireland long covered the activities of favoured interests uncritically.
The public hope that if media owners abuse their power then their competitors will reveal that abuse. Any unfairness may also be highlighted by the Press Council or other independent complaints tribunals.
For if a media owner puts pressure on employees to toe a particular line then he is unlikely to admit it publicly, and he might not admit it even to himself. The rich prefer to believe that their employees are nodding in agreement because they are witty and persuasive, rather than pushy and insistent.
Other kinds of influence are more complex. Serious findings of a tribunal seem likely to dog Denis O'Brien for the rest of his days, while for some, concerns persist about a Fianna Fail contribution given to Ray Burke by the subsidiary of a company in which Tony O'Reilly has significant interests.
How likely are the employees of any newspaper or station to feel free to pursue allegations against their company's shareholders as thoroughly as they might pursue allegations against people who have no stake in their company?
The rich invest in media for a variety of reasons, but making more money directly from the media is not necessarily the principal one. It may be as much about ego and influence. Some millionaires like to buy a football club. Others buy a newspaper or radio station, and then let politicians draw conclusions about what that ownership may mean if government policies on business do not please the media owners.
Media owners are often accused of abusing their power. Today, one of the proudest boasts of journalists in the USA is that they have won a Pulitzer Prize. But in his day Joseph Pulitzer was accused of lowering standards, and the term "yellow journalism" was coined to condemn his papers.
Critics found them trashy and sensational. He and his main competitor, William Randolph Hearst, were accused of using their power to provoke a US war against Spain in 1898.
And Irish politicians also courted such favour. When WT Cosgrave made the first American trip of any head of government of the independent Irish State, he said publicly that: "Ireland will never forget William Randolph Hearst, who has always been one of her best and truest friends."
In Britain, too, a range of press barons have come and gone, leaving fear and loathing in their wake. They included Northcliffe, Beaverbrook and Maxwell.
Ireland and the EU urgently need new laws on media mergers and takeovers in order to protect the public interest. And the public needs to know that bodies such as the Press Council and the BAI's Broadcasting Compliance Committee are easy to use by those who feel that the media is being unfair. They are open to everyone, including Denis O'Brien who has not chosen to bring to the Press Council his complaints about INM's treatment of his affairs.
The public takes a free media for granted, but it should not. Damaged by a severe advertising recession, and in some instances lumbered with debts, Irish media is vulnerable to manipulation.
And a reduction in the numbers and terms of employment of experienced journalists in the media means that there are fewer people on the inside to warn about adverse developments, or to organise resistance through the National Union of Journalists. In this context it is particularly worrying to see a journalist such as Sam Smyth singled out personally to bear the brunt of a defamation action.
But claims that radio stations owned by Denis O'Brien are setting a restricted news agenda have been vehemently denied as false and "outrageous".
There is no denying that some media owners set agendas, some more than others. Rupert Murdoch dropped the BBC from his Star satellite service in China to appease Beijing, and his cheerleading Fox News led a simplistic "War on Terror" in the USA that will cost that country both politically and financially for decades to come.
Eternal vigilance is the price of liberty. The Irish Government should bring forward overdue legislation to protect the public by ensuring a reasonable level of diversity in the ownership and content of media. Otherwise, Irish people's capacity to tell our own stories and to understand what is happening to us in the world may be greatly diminished.