The people who have executive power in the leadership structure of companies control what companies do. When ownership is diversified, business owners do not determine what their businesses do; your "tautology" is actually false, obviously so with more than a cursory examination of the world as it is. I myself am a part-owner of ARM, for example, but I have zero effective control over them.
And the question as to what should a company do is very definitely an ethical one. Some people try to argue that ethics only apply to companies in so far as they apply to the people that form the company; but others do not. Because the question isn't "what can a company do within the constraints of law", the question is actually what ought a company do.
Companies help match supply and demand where the supply or demand or both are divided and scattered enough that they can't be efficiently matched through individual contracts. But in this formulation, just like free markets, they have no moral content. The mere fact that there is demand for something does not imply that it is good that the demand is satisfied with supply. Lynch mobs frequently have short bursts of popularity, and they demand someone be lynched; irrelevant of whether they are legal or not, it should be clear that the fact of the demand does not amount to an ethical justification.
So when we ask what ought a company do, it is not enough to look at ownership structures; nor is it enough that we look at the operations of the company in providing supply to market demands. Merely following the law is not enough either; many immoral things are permitted by the law (to the point that later, the law changes), and many moral acts are taxed or prohibited by the law, for various formulations of morality. But more importantly, the law is itself informed by the ethical question over what ought companies do.
For example, it may be the case that child labour is legal in country X, and company A employs children in country X to meet supply for products in country Y, where such child labour is illegal and everybody agrees that it is unethical. By your formulation, there is no way to argue that company A is violating ethical norms. At best, you would suggest that shareholders - e.g. people with pensions, ultimately - should be held ethically responsible. You'll forgive me for thinking that that sounds rather ridiculous.
The people who have executive power in the leadership structure of companies control what companies do.
The leadership structure is determined by the Chief Executive, who is appointed by the Board of Directors, who are elected by the shareholders, i.e., the owners. Q.E.D.
(Lest you accuse me again of naïveté, I'm aware that there remains a principal-agent problem (http://en.wikipedia.org/wiki/Principal-agent_problem); when an angel becomes available to serve as CEO, I suggest doing your level best to get him the job.)
By your formulation, there is no way to argue that company A is violating ethical norms.
The whole point of my formulation is that it is silent on ethical questions. If you find it unethical that Company A uses child labor, you can buy from their competitors, or organize a boycott, or lobby to make their practice illegal—and I might well join you. Supposing that Company A is a standard joint-stock company, your actions would serve to align their interests (maximize value) with yours (be ethical according to your criteria). There is no conflict between your actions of protest and the statement "The company owners determine its actions"; as categories, is and ought are orthogonal.
should be held ethically responsible
Note the passive voice in this statement: "be held responsible". By whom? When people say that corporations should "be held responsible", what they means is, "We want to hold corporations responsible [is] according to our system of ethics [ought]." In other words, stripped of all camouflage, it is a naked grab for power. It's a generally well-intentioned power grab, of course, and depending on your system of ethics you might consider their achieving power to be a good thing. But Robespierre had good intentions, too, and the road to hell, etc.
You acknowledge the principle/agent problem, yet you pretend it doesn't exist in your QED; your demonstrandum was not convincingly demonstrated.
What if company A has a monopoly owing to being cheaper than any possible competition that does not use child labour? Would your argument for introducing a law against it not be an ethical argument governing the permissible actions of companies?
We want to hold corporations responsible [is] according to our system of ethics [ought]." In other words, stripped of all camouflage, it is a naked grab for power
Well yes, I do rather prefer government to anarchy. I'm sorry to say that if you see this as a "naked grab for power", I have little more to add, and am unwilling to continue a conversation with you. This is because, unless I'm mistaken, you are denying the very basis of democratic government ("we", the majority) in defense of something much more dangerous (the oligopoly of wealth and executive power). Someone who would do that is not someone I would trust; it is someone I'd rather shun.
the very basis of democratic government ("we", the majority)
Come now—you don't even believe this. The majority used to support legal chattel slavery. Did that make slavery right? Killing Native Americans and taking their land was pretty popular, too. And what about the overwhelming popular support for the Anschluss Österreichs that brought Austria under Nazi rule? Und so weiter.
You can believe in ethical government, or you can believe in the ethical principle of "majority rule", but you can't believe in both. Think about that the next time you slam someone for questioning "democracy".
If you shun me, it's not because I'm dangerous or untrustworthy, but rather because you are a Jedi and I am a Sith. (Suffice to say you've been exposed to a lot of anti-Sith propaganda.) Don't worry—I, too, was once a Jedi, and I don't take it personally. Luckily, it's never too late to come over to the Dark Side.
And the question as to what should a company do is very definitely an ethical one. Some people try to argue that ethics only apply to companies in so far as they apply to the people that form the company; but others do not. Because the question isn't "what can a company do within the constraints of law", the question is actually what ought a company do.
Companies help match supply and demand where the supply or demand or both are divided and scattered enough that they can't be efficiently matched through individual contracts. But in this formulation, just like free markets, they have no moral content. The mere fact that there is demand for something does not imply that it is good that the demand is satisfied with supply. Lynch mobs frequently have short bursts of popularity, and they demand someone be lynched; irrelevant of whether they are legal or not, it should be clear that the fact of the demand does not amount to an ethical justification.
So when we ask what ought a company do, it is not enough to look at ownership structures; nor is it enough that we look at the operations of the company in providing supply to market demands. Merely following the law is not enough either; many immoral things are permitted by the law (to the point that later, the law changes), and many moral acts are taxed or prohibited by the law, for various formulations of morality. But more importantly, the law is itself informed by the ethical question over what ought companies do.
For example, it may be the case that child labour is legal in country X, and company A employs children in country X to meet supply for products in country Y, where such child labour is illegal and everybody agrees that it is unethical. By your formulation, there is no way to argue that company A is violating ethical norms. At best, you would suggest that shareholders - e.g. people with pensions, ultimately - should be held ethically responsible. You'll forgive me for thinking that that sounds rather ridiculous.