I disagree, if the goal is make people think about ethics. (If the goal is to prevent people from ever doing unethical things, you're right that is unrealistic not only because of human weakness but because we do not all agree on what ethical behaviors include.)
I think it is a really good idea to encourage people to think about ethics, and to imagine in advance how they would respond to various situations. Boing Boing may have a high percentage of readers who are already thinking about ethics (it's an activist blog), but that approach to life is far from universal. When I was in school/grad-school I thought of professional ethics mostly as something other people had to worry about. My rationale was that as a physical science major my work was inherently ethically neutral (science is neither good nor evil) and that since we didn't have human subjects or provide goods or services to humans we didn't have much to worry about. Sure, doctors and business majors had to worry, but not us scientists, I thought.
I think it's easy when you spend most of your time working with THINGS instead of PEOPLE to forget that people nonetheless can be affected. Also, at least for me, it is helpful to remember that even though I am not a business 'decision maker', I am nonetheless empowered to be more or less ethical.
Now, I claim to know where I stand. I work in defense and long ago made a mental list of what I would and would not be willing to do (e.g., I won't design firearms, bombs, or other offensive weapons) and how close I'm willing to be to people who do these things. But if asked, would I be tough enough to choose unemployment? That's where some of the imagining and the mental roleplay is useful, so that I have a plan in advance, and failing that, at least more honesty.