The UK must not shy away from trying to resolve international crises despite the "terrible misadventure" in Iraq, a report from charity Oxfam argues.
Oxfam says the UK's Middle East policy fuels anger in the region
It warns that it would be disastrous if the country was put off sending troops to future humanitarian crises like those seen in Sierra Leone and Kosovo.
But Oxfam says the UK's power to be an international force for good has been undermined by foreign policy errors.
The government said its actions abroad in the past decade had been effective.
Meanwhile, a separate report by the Oxford Research Group (ORG) has warned that UK and US policy towards Iraq has "spawned new terror in the region".
The International Committee of the Red Cross also published a report on Wednesday which said every aspect of life was getting worse for ordinary Iraqis.
Four years after the US-led invasion, the ICRC says the conflict is inflicting immense suffering, and calls for greater protection of civilians.
The Oxfam report, A Fair Foreign Policy, argues that the positive effect of interventions in Sierra Leone and Kosovo should not be forgotten amid debate about Iraq.
An online survey of 2,374 adults conducted for Oxfam showed that 67% of people would support Britain sending troops "as a last resort to help stop genocide or mass war crimes".
It calls for foreign policy to refocus on protecting civilians, as well as challenging human rights abuses by friends as well as enemies.
But the report also says that attitudes towards the wider Middle East have led to "a disturbing trend of anti-Britishism" in many developing countries, based partly on a perception of double standards.
It cites the example of last year's conflict in Lebanon and the refusal by ministers to demand an immediate ceasefire.
Oxfam Director Barbara Stocking said her organisation had seen the "good and bad" effects of UK foreign policy around the world.
"However, it is now clear that the invasion of Iraq, and the government's failure to stand up to all governments when they break international law and harm innocent people, have seriously damaged Britain's capacity to be a force for good on the world stage," she said.
"The Iraq war was a terrible misadventure, but it must not cause future prime ministers to return to the caution of the previous Conservative government.
"That administration stood by while the genocides in Bosnia and Rwanda unfolded. We must say 'never again' as much to our failure to stop these atrocities, as to repeating Iraq."
A Foreign Office spokesman said: "We have rightly focused on 'hard' security issues such as Iraq, Afghanistan, Bosnia, Kosovo and Sierra Leone as well as 'softer' issues such as climate change and poverty eradication.
"We disagree that the UK now exercises less influence because of Iraq.
"On the contrary the UK remains at the heart of every major international debate and our influence as consensus builders is recognised worldwide."
Meanwhile, the ORG study argues that by including Iraq in the "war on terror", Britain and the US have "created a combat training zone for jihadists".
The strategy has also "emboldened" Iran, Syria and North Korea and led to a resurgence of the Taleban in Afghanistan, it said.
And it added that the continuing military action has increased the likelihood of terrorist attacks on the scale of 9/11.