The Prince of Wales viewed himself as a "dissident" working against political opinion, a former aide has said.
The prince believes the diaries were accessed unlawfully
The claim from Mark Bolland, a private secretary between 1996 and 2002, was contained in a statement released as the prince began a High Court case.
He took action after the Mail on Sunday published comments allegedly made in his journal about China's regime.
The prince's lawyers said he was entitled to keep personal documents confidential, like "anyone else".
"We say it is absolutely vital to the position of the claimant, and anyone else in his position, that this sort of document cannot be published willy-nilly by the press," said Hugh Tomlinson QC, for the prince.
Prince Charles claims eight diaries were copied by a former member of his staff and is suing the Mail on Sunday's owners Associated Newspapers for breach of copyright and confidentiality.
In extracts about the 1997 Hong Kong handover published in the Mail on Sunday in November 2005, the prince described Chinese officials as "appalling old waxworks".
In another reported extract, Prince Charles described one ceremony as an "awful Soviet-style" performance and dismissed a speech by then-Chinese President Jiang Zemin as "propaganda".
In his statement, Mr Bolland, who is expected to give evidence for the Mail on Sunday, said: "He would readily embrace the political aspects of any contentious issue he was interested in...
"He carried it out in a very considered, thoughtful and researched way. He often referred to himself as a 'dissident' working against the prevailing political consensus."
He said Charles later did not attend a state banquet thrown by Chinese President Jiang Zemin "as a deliberate snub".
He added: "He did not approve of the Chinese regime, and is a great supporter of the Dalai Lama, whom he views as being oppressed by the Chinese."
Mr Bolland's witness statement was released by the Mail on Sunday
But the prince's legal team, have denied he boycotted the banquet.
Mr Tomlinson and private secretary Sir Michael Peat have also denied the Mail on Sunday's assertion that the prince "campaigns on contentious issues".
Charles says the documents, including the 3,000-word journal he titled The Handover of Hong Kong - or The Great Chinese Takeaway, were unlawfully copied and wants the court to order their return.
Mr Tomlinson said Prince Charles had given copies of his private journals to family members, friends and advisers over the last 30 years in envelopes marked private and confidential.
"The claimant does not intend or wish to publish the journals although it is possible that after his death, edited extracts may be published," he said.
Mr Bolland said the journals were photocopied by a secretary and sent out to an array of the prince's acquaintances, including politicians, "media people", journalists, actors and friends, as a "bit of fun".
The former aide said he would be astonished if a comprehensive list of the recipients had been kept, but he thought 50 to 75 people would have received journal extracts, which he said were not treated in the same manner as confidential documents.
But Sir Michael said he had contacted all the recipients of the journal and been assured that copies had not been passed on to the Mail on Sunday.
Sir Michael said that whoever had passed the journals to the Mail on Sunday could not have received them legitimately.
"Past and present employees in the Prince of Wales's office have signed confidentiality undertakings. They could not legitimately have taken and distributed copies of the journals."
And he said no single journal had been sent to more than 46 people. Only one politician had ever received a journal and was a close friend of the prince, Sir Michael added.
Charles' legal team had originally intended to ask the court to keep Mr Bolland's witness statement secret.