I do not know any rational ground for this view, or perhaps, for the somewhat more rational view that whatever the majority desires is preferable to what the minority desires .... All that I can find to say on this subject is that an ethical opinion can only be defended by an ethical axiom, but, if the axiom is not accepted, there is no way of reaching a rational conclusion. ... It assumes that happiness is better than unhappiness. This is an ethical principle incapable of proof.
Source: The Autobiography of Bertrand Russell, v.3.
More info.: https://russell-j.com/beginner/AB31-250.HTM