Philosophers often use thought experiments in an attempt to refute some theory. In the particular case of ethical thought experiments, philosophers’ arguments tend to take this form:
1. Consider some unlikely situation.
2. In this situation, moral philosophy X says you should do Y.
3. Y is clearly immoral.
4. Therefore, X cannot be true.
In response, people who believe X often try to refute (2)—the idea that Y follows from X. In many cases, this is a mistake. Typically, the weakest point here is (3)—the assumption that Y is immoral. Even if we intuitively feel that Y must be immoral, our intuitions often misguide us; if we want to think clearly, we must apply rationality to our judgments whenever possible. We cannot reject a moral philosophy because of a thought experiment.
Intuitional and Rational Judgments
When making ethical judgments, people tend to rely heavily on intuition. An ethical system must contain some sort of intuition as the basis for a first principle; but it is important to select the right intuition. Most people who have not studied ethics (and even many who have) tend to act on whatever intuition they happen to feel in the moment, even if it contradicts some previous feeling.
When establishing an ethical theory, one should choose a few basic intuitions and then use rational principles to develop a consistent philosophy.
Once one selects some ethical framework, one can no longer make statements such as “Y is clearly immoral.” It must be proven immoral within the framework, not by our limited and often-inconsistent  instincts.
Below, I discuss three thought experiments that have been used to reject utilitarianism, and why they fail at this purpose.