It is not clear how to weight one preference against another, and fulfilled preferences are harder to add up than pleasure and pain.
There are different definitions of sentience, depending on who you ask.
Singer doesn't attribute full rights to unborn or newborn babies - there is major controversy over giving full preferences at 4 weeks old.
This theory gives rights to severely mentally ill people, who have had their rights taken away from them for the protection of both themselves and others. If they are unable to rationalise, should they really be given preferences?
This branch of Utilitarianism can go against common laws - for instance, abortion may be off limits if someone considers a foetus to be sentient, and thus capable of having preferences.

	Created by Summer Pearce almost 10 years ago

AS - Level (Year 1) Ethics (Utilitarianism) Slide Set on Preference Utilitarianism, created by Summer Pearce on 22/05/2016.