A finding that London's mayor breached a local authority code by making remarks to a Jewish reporter was "wholly untenable", his lawyer said.
Mr Livingstone said he was expressing his honestly-held view
James Maurici was appearing at the High Court for Ken Livingstone who is challenging a four-week suspension.
The Adjudication Panel for England made the ruling in February after finding he had brought his office into disrepute.
The mayor has described the punishment, which is frozen pending Wednesday's legal challenge, as inappropriate.
A three-man disciplinary tribunal unanimously ruled that Mr Livingstone was "unnecessarily insensitive and offensive" when he compared the Evening Standard's Oliver Finegold to a Nazi concentration camp guard.
But Mr Maurici quoted William Rees-Mogg's comment in The Times that the tribunal's decision was to "inflate trivial disputes of the late evening into matters of state."
He said: "Mr Livingstone has long held well-documented, lawful and, we say, political views as to the association of both the Evening Standard and its owners, Associated Newspapers, with far right-wing politics.
"Mr Livingstone suspected the Evening Standard's motivations for being at the reception in question."
It had been made "crystal clear" to the Evening Standard that it had not been invited to the reception and that Mr Livingstone regarded the newspaper's actions as tantamount to harassment, said Mr Maurici.
But the chairman of the tribunal panel, David Laverick, said it had decided on a ban because Mr Livingstone had failed to realise the seriousness of his outburst.
Mr Laverick went on to say that the complaint, brought by the Jewish Board of Deputies, should never have reached the board but did so because of Mr Livingstone's failure to apologise.
During legal argument, the judge said that Mr Livingstone's remark was "clearly offensive and intended to be so", but that it did not make it a breach of the code of conduct.
"I don't want anyone to suggest that Mr Livingstone is anti-Semitic", said Mr Justice Collins. "There has never been any indication of that. That is absolutely clear. No-one can think he was making a remark like that because of anti-Semitism."
If Mr Livingstone's appeal fails, he will be responsible for paying his own legal costs, estimated at £80,000.
But he has vowed to take the case all the way to the House of Lords even though it could cost "hundreds of thousands of pounds" if he loses.
The mayor accused the Board of Deputies of British Jews of making the original complaint only to try to "hush" him up over his views on the Middle East.
However the Board denies there was ever a witch-hunt against Mr Livingstone.