This passage from Mill's Autobiography seems, at first glance, to be a typical and unproblematic characterisation of his views on toleration. But, on closer inspection, it seems rather to be a slip, for the ‘only commendable’, indeed ‘possible’ toleration which Mill here mentions is that of opinion. Mill is, of course, equally celebrated for his arguments concerning toleration of all manner of individual conduct in the category which he styled that of self-regarding action. Even the two spheres of liberty of opinion and self-regarding action taken together do not exhaust the types of freedom and toleration which he championed, and regarded as analytically distinct.

Perhaps Mill wished to emphasise the grounds of the forbearance shown in observing liberty of opinion; the ‘conscientious sense of the importance to mankind’ might implicitly be supposed the same as that which requires the respect and toleration shown to individual diversity.