Utilitarianism and the wrongness of killing

Richard Henson has argued that hedonistic-average-act-utilitarianism has the extremely counter-intuitive consequence that certain individuals ought to be killed simply because they are unhappy and because their deaths would raise the average level of happiness. It is argued that Henson's criticisms are correct and that they can be extended to other versions of utilitarianism: total (as opposed to average) utilitarianism, non-hedonistic versions of utilitarianism, and those versions of act-utilitarianism that have originated in the recent controversy about population control.