It was not only the Opposition parties who voiced concerns - Government allies Peter Dunne and the Maori Party were opposed to the move and even Act's David Seymour had reservations.
Speaking after Prime Minister John Key announced the deployment in Parliament, Mr Little said troops were being sent into danger in Iraq with little hope of making any difference.
"They will not just be behind the wire, they will be exposed to the much wider conflict. It will not be just soldiers we send to Iraq -- it will be Kiwis travelling around the world."
Instead he urged more reconstruction work.
"We will not defeat - no one will defeat - Islamic State through the Iraq Army."
Mr Key was also criticised for refusing to allow Parliament a vote on the deployment.
NZ First leader Winston Peters said National knew it could not get a majority and there was no mandate for the action. He said Mr Key had earlier indicated a United Nations-backed action would be required for New Zealand to enter Iraq.
"Nothing has changed in Iraq except his 'club' persuaded Mr Key to commit our troops."
Mr Seymour said he had "considerable scepticism" about what any such intervention could achieve, but backed the decision in the interests of collective security and relations with New Zealand's allies.
Green co-leader Russel Norman said National was dragging New Zealand into the Middle East at the behest of "Washington, not Wellington".
"Every Western bomb dropped on the Middle East over the last half century has only added to the Isil recruitment queue."
Maori Party co-leader Te Ururoa Flavell said sending troops to train would be seen as an aggressive move by Isis.
United Future's Peter Dunne raised concerns about troops getting caught in an escalation of the conflict and said New Zealand should use its place on the Security Council to ensure any international action was sanctioned by the UN.
Mr Key responded to the criticism angrily, saying he believed Mr Little would send troops in the same circumstances if he was Prime Minister.
He warned that if a New Zealander fell victim to Isis, the leaders of Opposition parties could rue their choices.
"We all understand the domestic risks of Isil and we understand the risks for New Zealanders. And I just look forward to the political leaders who have spoken in opposition today being the ones to come forward if something goes wrong to those New Zealanders."
The chief of the Defence Force Lieutenant Colonel Tim Keating later said he had had to be sure the troops would be able to make an impact and that strong safety measures were in place before he could approve deployment.
- By Claire Trevett of the New Zealand Herald
