Former Afghan foreign minister Najibullah Lafraie said the latest death showed that SAS troops were not needed in the region.
In a live chat on nzherald.co.nz, Dr Lafraie said the SAS were contributing to instability in Afghanistan by carrying out violent military action.
He rejected an statement from Prime Minister John Key that pulling the SAS out of Afghanistan would put New Zealanders in danger of becoming victims of global terrorism.
"They don't make any positive contribution.
"I don't think there is a military solution to the problem in Afghanistan. I believe NATO forces have become part of the problem and cannot be part of the solution."
He said reports of the operation where Mr Smith was killed were "disturbing".
"The team seem to have been engaged in a night raid, similar to the ones carried out by the Americans, and focused upon in the past two years. Hundreds of innocent people have been killed or detained in such operations."
Dr Lafraie was involved in the resistence movement against the Soviet invasion of Afghanistan in the 1980s.
After the collapse of the Afghan communist regime in 1992, he was elevated to the role of Minister of State for Foreign Affairs in the Islamic State of Afghanistan.
He served in that position until 1996, when the Taleban captured Kabul.
Dr Lafraie spent 12 months in hiding from the Taleban regime. His brother was placed in a Taleban jail.
Despite that, he called for the US and NATO to involve the Taleban in a compromise political solution to conflict in Afghansitan.
"Unfortunately there cannot be a political solution without the participation of the Taliban. They seem to have learned from their past mistakes, and hopefully won't be as rigid as they were before. "
Details of latest death revealed
In a media conference this afternoon, Defence Force Lieutenant General Rhys Jones revealed Mr Smith was employed as a medic.
He had been the first to treat Corporal Grant when he was shot through the heart during an insurgent attack in Kabul last month. Corporal Grant, 41, was killed in an attack by the Taliban at the British Council offices in Kabul.
Lance Corporal Smith was one of 15 Special Air Service (SAS) soldiers who responded to information about a planned attack in the Afghan capital.
The SAS team, which was supporting the Afghan Crisis Response Unit, was attacked as it tried to cordon off a compound in Wardak province near Kabul, where the insurgents behind the planned attack were believed to be.
Lt Gen Jones denied media reports that the operation was a response to a family dispute, but had been planned over several days in response to information that the compound was housing a suicide bomber.
He said one insurgent was killed in the assault and another was arrested. Both were named as people of interest in the arrest warrant that was issued.
A girl who was injured by shrapnel in the firefight was recovering.
Lance Corporal Smith enlisted in 1999 and first served in Afghanistan in 2010.
He was single with no children but left his mother, grandmother and two brothers in Wellington, and his father and grandparents in Tauranga.
A family statement read: "Leon was loved by his family. He was also loved by his friends and his comrades. He was a wonderful grandson, son, brother and friend to many. He was sincere and genuine.
"Leon was proud to serve in the NZ SAS. He believed in what he was doing, and we supported him in what he did.
"We are grieving the loss of Leon. We ask for our privacy to be respected at this very difficult time. Rest in peace Leon.''
Prime Minister John Key yesterday said Lance Corporal Smith had "paid the highest price for his service to this country and we will mourn his death".
"His death, however, does not alter our commitment to helping Afghanistan. It continues to be the Government's intention to keep the SAS in Afghanistan until March as planned."
The PM said he deeply regretted Lance Corporal Smith's death, "but I don't regret the decision that we made to commit the SAS to Afghanistan".
"I think they are playing their critical part to free the world from global terrorism."
The SAS is on its fourth deployment to Afghanistan since the US-led invasion in 2001.
Replay our live chat with former Afghan foreign minister Najibullah Lafraie from earlier today.
