Ken Livingstone's remarks to an Evening Standard journalist risks "endangering public confidence in local democracy", the High Court has heard.
The mayor is challenging a decision by the Adjudication Panel for England that his comments breached the Greater London Authority's code of conduct.
His lawyers say the decision was legally flawed on a number of grounds.
But Tim Morshead, appearing for the Ethical Standards Officer, says his comments were irresponsible.
The exchange with Evening Standard journalist Oliver Finegold happened in February last year as the mayor left an event marking 20 years since Chris Smith came out as the first gay MP.
'Holocaust horrors'
Mr Livingstone likened him to a Nazi concentration camp guard when Mr Finegold revealed he was a journalist at the Evening Standard.
Speaking at the High Court, Mr Morshead said: "With us in this city are survivors of Belsen and Auschwitz. The holocaust and its horrors are not a mere memory. They live with us and are among us.
"Remarks like Ken Livingstone's, if unchecked, tend to endanger public confidence in local democracy.
"Londoners, whether or not they voted for Ken Livingstone, are entitled to expect that their mayor will conduct himself to high standards, suitable to the high office to which he has been elected."
Mr Livingstone 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.
He has accused the Board of Deputies of British Jews of making the original complaint 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.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~51~RS~)