That may have been what the article was about. Once the student was suspended, the experiment was about the refusal.
Let me clarify. It is appropriate to give grades for the participation in the experiment. If, as part of his research (and that is what it was), he wishes to tabulate how many people will step on a paper with Jesus' name written on it, that's acceptable. If a student refuses to participate in the experiment, he can be denied a grade. This is done in psychology classes all the time, like when an entire class is given a socialization test. In a psychology of religion test, for example, it is a fair question, "if you had to give an electric shock a Christian or a Moslem, who would it be".
If the student is denied a grade for refusing to step on a paper with the name of Jesus on it, that is against public policy, and should not be tolerated. This is the same as a student in a psychology class being denied a grade for actually refusing to give the electric shock. Such subjects are routinely paid for this type of participation, and grades are never questioned.
My wife once had a psych class with a new instructor who attempted to slap students to get their reaction. My wife had reported the man (being a teacher's wife helps) but got no action, due to tenure. The next time he came around to her, she simply threatened to put him through the wall if he tried it to her. That settled it.
The man's job will be protected by tenure, but students should stop enrolling in his classes.
I read the OP again to make sure I was clear on what happened. The textbook exercise made it clear that the purpose of the lesson was to illustrate that most students do not wish to step on the name of Jesus, and ask why. This is an excellent exercise. The teacher not only violated the student's constitutional rights, but violated the instructions in the textbook as well.