Full Idea
There are some forms of utilitarianism which aim to be entirely 'value-free' or empirical, such as those which define happiness in terms of the satisfaction of actual desires or preferences, regardless of their content.
Gist of Idea
Preference utilitarianism aims to be completely value-free, or empirical
Source
Rosalind Hursthouse (On Virtue Ethics [1999], Ch.1)
Book Reference
Hursthouse,Rosalind: 'On Virtue Ethics' [OUP 2001], p.37
A Reaction
This point makes it clear that preference utilitarianism is a doomed enterprise. For a start I can prefer not to be a utilitarian. You can only maximise something if you value if. Are preferences valuable?