> Because they have a responsibility to act in the best interest of the corporation

Agreed.

> (which is as far as I'm concerned equivalent to the best interest of the shareholders with respect to the corporation...)

That's both an exceedingly simplistic mental model and quite a difficult-to-prove assumption of equivalent interests. Surely you can think of some very simple counterexamples where the corporate interests and shareholder interests frequently do not align.

Take the vast majority of Apple's history, for example—under Steve Jobs, Apple's purpose was to delight customers first, and leave benefits to other stakeholders, including shareholders, as a byproduct of achieving that purpose. From 1995-2012, Apple paid no dividends to shareholders. Sure, its stock went up, and shareholders who sold stock bought at earlier low per-share prices realized a return. But there's pretty much no question that for 17 years, Apple's interests—as understood and pursued by Jobs—did not align very well with shareholder interests. Jobs certainly never made decisions based on what was in the shareholders' best interests.

Or consider investments into R&D, which frequently are not in the best interests of the average shareholder—who often do not retain their shares over long enough periods of time where R&D investments (which are in the company's best interest) might actually align with shareholder interests (where massive capital expenditures are not, instead, returned as dividends).

Moreover, there are companies whose directors or owners might think their social and environmental responsibilities trump those of shareholders looking to make a buck. They may run a company in a way that feels responsible to them and in the company's best interest, while shareholders may vehemently disagree with those decisions.

In short, shareholders are responsible for looking out for their own interests. The companies they invest in are not, and cannot, focus[ed] on the shareholders' best interest. It really seems like you've somehow conflated a corporation into some kind of entity that is more like a democratically elected representative government whose job it is to represent and realize the interests of the electorate. That's simply the wrong mental model to have about corporations.

Have you spent much time studying the kinds of companies that are out there who make their shareholders' interests their primary motivation and concern? They are almost universally focused on meeting short-term demands and expectations. They often do not ever seem to follow any kind of long-term vision that leads to Big Things™ ... instead, they try to squeeze every last extra bit of dollar value out of the corporation to return it to stakeholders. Bluntly put, few of those companies are loved by their customers. And there are more people than Steve Jobs who believe a corporation's responsibilities ought to be focused on their customers over shareholders.

> It isn't in the best interest of the corporation to unnecessarily give more money to the IRS than what they explicitly require.

Says who? shawnz on HN? You may hold that opinion, but that carries with it quite a lot of assumptions and ideological baggage, which seems to mostly center upon the notion that a corporation's best interest is to capture and retain as many dollars as it can, society be damned. I'll agree that the last few decades of corporate activity in the US increasingly reflects such a perspective to a worrisome degree. But that's just a matter of perspective. There's zero legal obligation to take advantage of the market the government takes great pains and expense to define, protect, and advance and then avoid paying as much tax as you can get away with. Sure, there are all kinds of deductions and loopholes out there to make billions and pay $0 in taxes if you want it. But nobody is making corporations do that. You seem to believe there is some kind of definitive corporate best interest. There is not. They're a legal vehicle for engaging in commerce in concert with others, while enjoying the legal protections built into the market and held there by faith in the government to do its job continuing to advance and protect the interests of commerce. It's not crazy to imagine that a corporation's best interests can also include paying a reasonable share of taxes without a bunch of avoidance schemes. For example, stop taking certain deductions. Or perhaps refuse to park money in a foreign tax haven just because you can. It isn't unreasonable to expect a corporation consider social and environmental responsibility part of its best interests, instead of an annoying cost to avoid no matter what.

> I don't understand how this distinction between shareholders and corporation comes into play at all.

The distinction comes into play because, again, you argued "Corporations have a responsibility to act in the best interest of the shareholders, which includes not unnecessarily choosing to pay more taxes than you need to." Your argument about that responsibility was wrong. I wasn't actually trying to engage the tax question at first (though now I obviously am addressing it further to some extent). I am, however, primarily interested in helping you correct and update an invalid mental model about corporate responsibility to shareholders. Which is why I asked you—if you accept there is no such corporate responsibility to shareholders "best interests", then what's the argument for why a corporation is obligated to engage in as many tax avoidance schemes as they possibly and legally can so as to not pay one penny more than they could by engaging in all such schemes?