You seem to be confused about ethics. Behaving ethically is not defined by anyone else's ability to prove that you did or did not behave ethically.
Looks like you didn't understand me. You're confusing the "ethic" aspect of my answer with the "legal" aspect. I mean "enforcing legally the respect of robots.txt is abusive and unethical.". I mean too "I can't imagine that you'd be legally in trouble for web-spidering, for personal use, without taking care of robots.txt, except in China or Iran.". I never meant "Go suck all websites you want to and don't bother", ever.
I think too the generalisation "if you use a web-spidering program without taking notice of robots.txt, you're ethically wrong", is questionable. Ethics aren't that simple. Perhaps he's a political refugee trying to extract important information from some hostile hidden website. Is he "right" or "wrong"?