BKS Iyengar says backbends address fear. Why do you think that is?

I agree , whole heartedly whether it is as backbend or handstand or doing any inversion on your own for the first time without wall assistance tends to raise the fear factor . We all have different threshold buttons for fear . I personally love backbends and hip openers but for some reason tripod headstand weirds my neck out. When we go upside down or bend we are pushing past our control boundry. We are like "uh-oh" I might lose control here and when we are in a classroom setting this
can be a major source of uncomfortability. The other is " holy dirt " I might really be awful at this. We are built different , with different injuries so the flag might come at any moment. The real joy comes when you over come that on the mat you not only reach a different place in you practice but in your courage too.