What purpose can be served by empirically unsubstantiated speculation in ethics? In answering that question, we need to distinguish between the major branches of ethics. In foundational moral philosophy, the use of speculative examples is warranted to the extent that ethical principles and theories are assumed to be applicable even under the extreme circumstances referred to in these examples. Such an assumption is in need of justification, and it cannot just be taken for granted. In applied ethics, the use of (...) unrealistic scenarios is more difficult to justify. It can be positively harmful if it diverts our attention from more urgent issues. Neuroethics is one of the areas of applied ethics where speculative scenarios have taken up much of the attention that could instead have been devoted to problems that are relevant for the treatment and care of patients. Speculative ethics has often been defended with mere possibility arguments that may at first hand seem difficult to refute. It is shown with examples how such claims can be defeated with a combination of science and argumentation analysis. (shrink)