It's possible for specific people inside a corporation to behave in unethical ways. However, the definition of maximizing shareholder value is not simply "make the stock price as high as possible in the short term." It's perfectly possible for executives in a corporation to take the high road as the optimal strategy for maximizing shareholder value.
Thankfully, ethics do not depend on the existence of a soul nor conscience. There is a such thing as emergent behavior, after all.