In complex, pluralistic societies, different views concerning the moral duties of healthcare professionals inevitably exist: according to some accounts, doctors can and should cooperate in performing abortion or physician-assisted suicide, while according to others they should always defend human life and protect their patients’ health. It is argued that the very plurality of responses presently given to questions such as these provides a liberal argument in favour of conscientious objection, as an attempt to deal with moral diversity by protecting both (...) the professionals’ claim to moral integrity and the patients’ claim to receive lawful and safe medical treatments. A moderate view on CO is defended, according to which none of these claims can be credited with unconditional value. Claims to CO by healthcare professionals can be justified but must be subjected to a reasonableness standard. Both the incompatibility of CO with the medical profession and its unconditional sanctioning by conscience absolutism are therefore rejected. The paper contributes to the definition of the conditions of such reasonableness, particularly by stressing the role played by conceptions of good medicine in discriminating claims to CO; it is argued that respecting these conditions prevents from having the negative consequences dreaded by critics. The objection according to which accepting the physician’s duty to inform and refer is inconsistent with the professed value of moral integrity is also discussed. (shrink)