What did Elie Wiesel mean when he said indifference is the greatest source of evil and danger in the world?

I think he meant that if one is not decisive and willing to speak out against what is wrong, then he or she is only helping the cause spread. Ultimately causing danger and evil to occur as opposed to preventing it.

Or maybe if you cannot think for yourself, you are more susceptible to be influenced by greater powers, like Hitler and his maniacal plan to wipe out the Jews and create the "perfect race".