"nobody seemed to think it was a problem as far as I know"

This seems to me to be exactly the problem. How on earth do we know why someone might be picking this stuff up? Are they simply some parent who doesn't want their kids finding it? Do they intend to turn it in to CF? Those scenarious are equally as valid as somone picking it up to make an IED. The simple fact is we don't know, so how do we justify killing them without any further information?

This is an example of a "type 1" or "false positive" error. If/when we make a mistake in this situation, we have set up a situation where we kill people innocent of any crime. The type 1 error is morally worse than the "type 2" or "false negative" error - which is why our entire justice system is based on the premise of "relasing 10 guilty men before 1 innocent man goes to jail."

Are Iraqi civilians worth less than this? Do we allow our fear of attacks on our soldiers to push us to create situations where we reduce risk to ourselves by accepting, if we're wrong about the intentions of those picking up the materials, the deaths of innocent people? That's not what I thought I the value of "courage" meant. And it's not "choosing the harder right." I hope we stop this, and soon.