A man who allegedly sent offensive letters to the families of soldiers who died in Afghanistan has told the High Court that wounding someone's feelings is not a criminal offence.

Man Haron Monis, also known as Sheik Haron, wants the court to quash multiple indictments alleging he used the postal service to offend the families of fallen diggers as well as relatives of a trade official killed by a bomb in Jakarta.

Lawyers for Mr Monis and his co-appellant, Amirah Droudis, told the court today the relevant section of the Commonwealth Criminal Code was invalid because it infringed the implied constitutional freedom of political communication.

The letters were critical of Australia's involvement in Afghanistan and denigrated the deceased soldiers.

One said the Australian nation was to blame for the 2009 bombing in Indonesia because it was silent about the government's "oppressive behaviour" overseas.