I think most, but not all, people will try to do the right thing and help others in need, whether it is to help defend someone or to intervene on someone's behalf. At least most of the people I know would.

One night my friends and I saw this guy skulking around a car. It looked really suspicious like he was going to try and steal it. So we went around the in different directions, converged on the guy at the same moment to stop him from stealing the car. We scared the cr@p out of him as he was peeing in the shadows behind the car. It was funny, but not for him, so we apologized and went on our way. But we did what we thought was the right thing at the time.