It's a great point, but I think corporations have shown they're willing to sacrifice long-term benefit for next quarter's numbers.
The problem is that self-interested thinking doesn't often benefit the whole. Every corporation is in the right for cutting costs, reducing tax burden, and getting as much profit as possible (and keeping it!). Without a strong government to form and enforce public policy, the private sector creatively destroys itself and society every few decades, while the rich keep their cash.
Some on HN the other day speculated that the fiercely autocratic Asian governments are the only way to reign in the power of major corporations. I think there is a point to that.