I don't know about this... I opened up a can of worms in one of my photo classes as I offered a blind homeless person a hot coffee in exchange for a couple of photos of him playing guitar with his dog sleeping next to him.
What were the particulars of the assignment?
If the assignment was more "photojournalism" in that the intent was to capture the natural candid scene, I can understand the push back. However, if there were no restrictions, there should not have been a problem.
I wonder how many of your fellow students would have just taken a picture of the blind man and not even told him about it?