> A corporation's fiduciary duty is to its shareholders, not to its customers

This is a myth.

Firstly, corporations don't have fiduciary duties. Corporate officers, directors, and employees who act on behalf of the corporation, have fiduciary duties.

And those duties (in the US, as far as I understand it) amount to putting the company's interests above their own and making responsible, informed decisions. That doesn't mean always putting the interests of the shareholders before the customers. Its a judgement left to the people acting on behalf of the corporation - as long as they can show that their decisions are reasonable and not made out of self-interest.

Edit to add: This is also the basis for Corporate [Social | Environmental] Responsibility. People with fiduciary duties can reasonably decide that it is in the interest of a corporation for it to behave in certain ways within some wider context, even when that behaviour is not directly profit- or advantage-seeking.