I don't see that as a common argument. It exists, certainly. I think there are levels of thinking along these lines:
1. It's all Piazza's fault.
2. Piazza should share blame with his parents who were lousy parents.
3. Piazza, his parents and the frat should be blamed, not PSU.
4. Piazza and the frat should be blamed, not PSU.
5. Piazza, his parents, the frat and PSU all share some level of responsibility.
6. Piazza, the frat and PSU all share some level of responsibility.
7. The frat and Penn State should have know better. It's their fault.
8. The frat is 100% at fault -- put them all in jail.
9. PSU is Hell -- burn it to the ground.
And then just looking at the punishment:
1. Piazza was an adult making an adult decision. The frat boys shouldn't be punished.
2. Piazza was an adult making an adult decision. But the frat boys should be punished to some extent.
3. The frat boys let him die. Throw the book at him.
And many more ideas fit between the lines as well. This is a discussion. None of us have 100% of the details. Therefore, all opinions should be considered to some extent.