You’re not brave. Men are brave.
Bravery is when you’re afraid but you act anyway. Either your rational mind takes control or your moral sense overpowers your fear.
Batman isn’t accusing Superman of being a coward, he’s actually saying Superman can’t be brave. You need to be afraid to be courageous.
Seneca made a similar point:
A god has nature to thank for his immunity from fear, while the wise man can thank his own efforts for this. Look at that for an achievement, to have all the frailty of a human being and all the freedom from care of a god. – Letter LIV