Some of it does apply to all companies. But it a discussion that has both banks and investment banks, the distinction is an important one. Critical, even. They serve very different functions in the financial service sector. Glass-Steagall prevented commercial banks from owning or operating as investment banks. Repealing that seriously increased the risks of damage to the economy that investment banks can cause. That was far from the only, or even the most important, issue that led to the financial crisis. But it was certainly a major one. Before that, when investment banks operated as only partnerships, then all the capital they put at risk was the capital of the partners, who were the managers. Firms like Bear Stearns were known for their strong controls of the risks the firm took. But once they became publicly traded, and the capital at risk was not the capital of the managers, then very, very, quickly lost all semblance of understanding what risks they were running.
And the risks were not just to that company. The risks were to everyone. To the economy as a whole.
The risk to the economy of publicly traded investment banks is simply too high to be acceptable. No one should be allowed to have that kind of power to endanger others out of simple recklessness.