IMHO it is unacceptable that soldiers should be placed at this risk. There should be consequences for those who failed to see this risk.
You don't have to look for scapegoats. The risks are known, and yes, even junior troops are taught to acertain then. How far they go after being taught is a different matter, but at some point you cannot guard against all possible green-on-blue opportunities ... every moment. Nothing would get done.

It's totally acceptable that there are occupational hazards.

There is a mission with inherent risks to it, thus part of the nature of war.