I Do Mean It And You're Missing The Point
The level of doubt your are willing to tolerate is proportional to the number of innocents you protect. As long as the number of people protected is far more than those harmed as innocent unintended or mistaken casualties you have done more good than if you simply took no action and let all the people you could have protected perish. My comment about our system not applying is not that no evidence is needed, but rather the standard of evidence is not necessarily the same. The reason is that the risk of inaction is far higher than letting a single murderer go unpunished.
Regards,
Mark