You wouldn't have to suppress a fear system in order to help others if your fear system recognizes the value to one's own self in helping your (perceived) tribe, or the potential danger in either tribe members being harmed, or in losing the tribe's trust in you, or your perceived value to them. It wasn't very long ago that being ousted from your group meant certain death.

I think we underestimate how hundreds of thousands of years of surviving against superior predators and harsh environments through cooperative means has contributed to our brain's survival mechanism's complexity.