It is one of the drawbacks to asceticism that it sees no harm in pleasures other than those of sense, and yet, in fact, not only the best pleasures, but also the very worst, are purely mental. Consider the pleasures of Milton's Satan when he contemplates the harm that he could do to man. As Milton makes him say:
The mind is its own place, and in itself
Can make a heav'n of hell, a hell of heav'n.
and his psychology is not so very different from that of Tertullian, exulting in the thought that he will be able to look out from heaven at the sufferings of the damned.
Source: Bertrand Russell: Ideas That Have Harmed Mankind，1946.
More info.:http://russell-j.com/beginner/0861HARM-040.HTM