People will do "evil"(as harming allies) if:

1) they are unsustainable (like harming allies) - not sure can be fixed

2) Don't have enough knowledge(broken perception) to do differently.

3) ROI of doing evil is too high.

etc.

Could you point to scenarios where aknowledging non-existence of free will could help us? IMO it doesn't matter.

EDIT: Actually I think that existence of concept of free will is positive because it makes people compute choices better (even assuming free will does't exists and computation is deterministic)