[mitchdoogle]

I think you have it backwards. This kind of reasoning is actually why people do thought experiments. If you don't consider anything else, then the answer to the original problem is an easy math problem - one person getting killed is better than five people getting killed. It's only when you start making considerations that the thought experiment starts to gain value as a tool. Do I have more responsibility for acting rather than not acting? Who are these people anyway? Why are they there? You start asking yourself these questions and thinking about how your answer to the problem changes with them and it helps you to understand how you (and others) actually make ethical choices in the real world, which is the whole point, in my opinion.