Perhaps I should begin with a warning—you know the sort of thing; we see them at the start of certain television programs: “Viewers are warned that this presentation contains expressions so disgusting that a bullock-driver might blush”. Or: “Some of the scenes following are so revolting that no one with a trace of sensitivity would have filmed them in the first place”. One would like to think that those tactful cautions are displayed so that the innocent or the unwary do not fall into occasions of sin. But they may only be disguised promotional aids; it is not hard to…