"Positive utilitarianism recommends the promotion or maximising of intrinsic value, negative utilitarianism recommends the reduction or minimising of intrinsic disvalue. At first sight, the negative kind may seem reasonable and more modest in what it recommends. But one way of ending human misery is by putting all human beings out of their misery. This course of action is usually considered unacceptable. This has led to a search for reformulations of negative utilitarianism, or to its rejection."
The Penguin Dictionary of Philosophy
ed. Thomas Mautner
The Pinprick Argument
'Better Never To Have Been'
R.N. Smart's reply to Popper
Negative Utilitarianism FAQ (NU Study Group 2015)
Utilitarianism On The Net