[geofft]

Sure it is; that's why it's called "due diligence". You are legally required to engage in some amount of diligence when acquiring a company. As a very related example, a US company acquiring a foreign company is obligated to make sure the foreign company isn't engaged in corruption/bribery, and is expected to show a certain amount of competence in investigating the foreign company before the acquisition. Going ahead with the acquisition after an incompetent examination is illegal.

More generally, the law recognizes the concepts of negligence, reckless endangerment, a "reasonable person," the idea that you're responsible if you "knew or should have known" about some problem, etc., all of which I would classify as specific ways of stupidity and incompetence being illegal. Of course if you keep your stupidity and incompetence entirely to yourself, you're fine. But if you act stupid or incompetent in a way that affects other people or the public, chances are high that you're in legal trouble.