Not just under our own apparatus – it’s also the case under the ideals of knighthood. A true knight is supposed to uphold their vows at all costs and no matter the consequences – which points to GRRM’s romantic/existential leanings. And the oath of knighthood explicitly states that:

“In the name of the Warrior I charge you to be brave. In the name of the Father I charge you to be just. In the name of the Mother I charge you to defend the young and innocent. In the name of the Maid I charge you to protect all women.”

The Mother’s clause points to the fact that  Rickard and Brandon were innocent (and helpless, given their chains) until proven guilty; the Father’s clause reminds us that the laws of men and the laws of the old gods and the new state unequivocally that they had the right to a trial and killing them without one is murder; the Warrior’s clause demands that Jaime fight for the right no matter the odds. 

And yes, it’s not easy. As Jaime points out, there were dozens of knights in that room, many of them of great reputation, who did nothing, who put their oath of obedience above their oath of knighthood. But true kngihts are rare precisely because it is so difficult to put your ideals ahead of all practical considerations. Remember Dunk at the Tourney of Ashford and how rare it is to find a knight who remembers his vows; remember Brienne’s desperate fight against the Bloody Mummers or Jaime’s suicidal leap into the bear pit.