Forget about shoulds and look at reality. I'm talking about responsibility and how it works.
For example, I think that the water should be dry, and when I step into it, I am not responsible for getting wet on the account of my "should" thinking. Does it work like that in reality? No, it does not.
Ask yourself: can customer behavior patterns influence the direction of Sony as a corporation? For example, can a boycott influence Sony's attitude at the executive levels? I think the answer is that a real boycott does have such an ability. So to the extent customers have the ability to influence corporate behaviors, the customers become responsible for exercising that ability with due diligence.
At the same time, does Sony need to wait to get boycotted in order to improve their behavior? Of course not. What does this mean? It means Sony holds a primary proximate responsibility for their own behaviors. Sony executives have more influence over what Sony does than do all the Sony customers put together. At the same time, the amount of influence the Sony customers have is not zero.
So this is a correct and balanced way to understand responsibility. Responsibility is always commensurate with the power you have to influence something. The more power, the more responsibility you have. And our or your power can get as low as epsilon, but never absolute 0. So we always have some responsibility for everything, however tiny it may be.
So it's not "all like this" or "all like that." The reality is somewhere between what you're talking about and what your opponent is talking about. I would say Sony has about 70% responsibility to govern its own behaviors in a moral way and all the customers put together have about 30%, roughly. You can even see it as a 50/50 split, but you have to remember that the customer side of the 50 is shared out among all the customers, while the Sony side is concentrated in the hands of the very few powerful executives.