Imagine you're in some Banana Republic and the Dictator offers you to play his version of Russian Roulette:
You get a revolver and are asked to aim at someone innocent in his country and pull the trigger. He says there are few bullets in the revolver, but you're sure at least one chamber is empty. You'll never justice there or at home if you kill somebody like this. In case you pull the trigger and there's no bullet fired, the person you aimed at would become multi-millionnaire in some meaningful currency; very rich. But you would have killed the person if you aimed, pulled the trigger and there was a bullet aligned with the barrel. Either way, you would need to pay a week's worth of income.
Would you aim, and pull the trigger?
Presumably you would not.
Now imagine a different situation. You're leader of your country and hear the news that ethnic cleansing and massacres are happening in some other country. You cannot know for sure. Such things happen, but disinformation happens as well.
Some people suggest you should intervene with your military, and you know you would get away with it if it turns out that there was no ethnic cleansing or massacres, but merely a small insurgency about to be quelled.*
You realise that if there's evil going on you could help the people much, but if you were misled your intervention would really be a war of aggression, harming a great many people.
Either way, the fiscal and human costs to your country would be substantial.
Presumably interventionists would,
because people simply almost never change their mind
no matter how painful a cognitive dissonance I create. ;)
In dubio pro reo. Civilized countries employ this principle on the level of individuals. I think it is underappreciated on the level of countries. Too many wars have been started for manufactured reasons, and the costs of these wars have been horrible. Even supposedly very sophisticated countries** are susceptible and can be enticed to make the mistake of going to war on feeble grounds. It's almost as if a jury of ten would only need six "guilty" votes to convict the defendant, or even only four if the chairman of the jury is in favour of a conviction.
This is stupid. Uncertainty, fallibility and special interests working to deceive should be more widely recognised as corrupting our decision-making in such cases, and we should be careful accordingly.
*: With rural people fleeing from their villages when there's fighting (and returning after the war reporters left the scene) and the massacres are really insurgents killed by security forces, stripped of their weapons before the war reporters made their photos.
**: Including Germany..