  Even opponents of the yuck factor must concede that, sometimes, we know that an action is wrong merely on the basis of our reaction to it, even if we cannot satisfactorily justify that reaction. We know it is wrong to kill a healthy person so that his organs can be transplanted to save five lives, even though we presently lack any theoretically satisfactory way of distinguishing that case from the various trolley cases prominent in the killing/letting-die literature. (See Kamm (2006) for recent discussion.)