First, I agree with your conclusion. The way to address this is to change the law, pushing individual corporation is ineffective.

However, you DON'T have to maximize your profits above all other corporations. There's no such actual fiduciary duty and there never could be. That's the point the poster is trying to make - something being legal doesn't make it ethical and acting in a unethical, but legal, manner does not absolve you of contempt.

If you have no competition, you do have the luxury to choose between profitable and ethical. But if you have fierce competition, there isn't always a choice - market forces will drive out the more principled operators of business in favor of those that are more ruthless.