The omission bias is an alleged type of cognitive bias. It is the tendency to judge harmful actions as worse, or less moral than equally harmful omissions (inactions). It is contentious as to whether this represents a systematic error in thinking, or is supported by a substantive moral theory. For a consequentialist, judging harmful actions as worse than inaction would indeed be inconsistent, but deontological ethics may, and normally does, draw a moral distinction between doing and allowing.[1]
Spranca, Minsk and Baron extended the omission bias to judgments of morality of choices. In one scenario, John, a tennis player, would be facing a tough opponent the next day in a decisive match. John knows his opponent is allergic to a food substance. Subjects were presented with two conditions: John recommends the food containing the allergen to hurt his opponent's performance, or the opponent himself orders the allergenic food, and John says nothing. A majority of people judged that John's action of recommending the allergenic food as being more immoral than John's inaction of not informing the opponent of the allergenic substance.