Objectives: The mental health legislation of most developed countries includes either a dangerousness criterion or an obligatory dangerousness criterion (ODC). A dangerousness criterion holds that mentally ill people may be given treatment without consent if they are deemed to be a risk to themselves or others. An ODC holds that mentally ill people may be given treatment without consent only if they are deemed to be a risk to themselves or others. This paper argues that the dangerousness criterion is unnecessary, unethical and, in the case of the ODC, potentially harmful to mentally ill people and to the rest of the community. Methods: We examine the history of the dangerousness criterion, and provide reasoned argument and empirical evidence in support of our position. Results: Dangerousness criteria are not required to balance the perceived loss of autonomy arising from mental health legislation. Dangerousness criteria unfairly discriminate against the mentally ill, as they represent an unreasonable barrier to treatment without consent, and they spread the burden of risk that any mentally ill person might become violent across large numbers of mentally ill people who will never become violent. Mental health legislation that includes an ODC is associated with a longer duration of untreated psychosis, and probably contributes to a poorer prognosis and an increase risk of suicide and violence in patients in their first episode of psychosis. Conclusions: Dangerousness criteria should be removed from mental health legislation and be replaced by criteria that focus on a patient’s capacity to refuse treatment.