Alas, poor slandered, slaughtered Midianites, to be remembered only as poetic symbols of universal evil in a Victorian hymn.

The rival god Baal seems to have been a perennially seductive tempter to wayward worship. In Numbers, chapter 25, many of the Israelites were lured by Moabite women to sacrifice to Baal. God reacted with characteristic fury. He ordered Moses to 'Take all the heads of the people and hang them up before the Lord against the sun, that the fierce anger of the Lord may be turned away from Israel.' One cannot help, yet again, marvelling at the extraordinarily draconian view taken of the sin of flirting with rival gods. To our modern sense of values and justice it seems a trifling sin compared to, say, offering your daughter for a gang rape. It is yet another example of the disconnect between scriptural and modern (one is tempted to say civilized) morals. Of course, it is easily enough understood in terms of the theory of memes, and the qualities that a deity needs in order to survive in the meme pool.

The tragi-farce of God's maniacal jealousy against alternative gods recurs continually throughout the Old Testament. It motivates the first of the Ten Commandments (the ones on the tablets that Moses broke: Exodus 20, Deuteronomy 5), and it is even more prominent in the (otherwise rather different) substitute commandments that God provided to replace the broken tablets (Exodus 34). Having promised to drive out of their homelands the unfortunate Amorites, Canaanites, Hittites, Perizzites, Hivites and Jebusites, God gets down to what really matters: rival gods!

I know, yes, of course, of course, times have changed, and no religious leader today (apart from the likes of the Taliban or the American Christian equivalent) thinks like Moses. But that is my whole point. All I am establishing is that modern morality, wherever else it comes from, does not come from the Bible. Apologists cannot get away with claiming that religion provides them with some sort of inside track to defining what is good and what is bad — a privileged source unavailable to atheists. They cannot get away with it, not even if they employ that favourite trick of interpreting selected scriptures as 'symbolic' rather than literal. By what criterion do you decide which passages are symbolic, which literal?

The ethnic cleansing begun in the time of Moses is brought to bloody fruition in the book of Joshua, a text remarkable for the bloodthirsty massacres it records and the xenophobic relish with which it does so. As the charming old song exultantly has it, 'Joshua fit the battle of Jericho, and the walls came a-tumbling down. There's none like good old Joshuay, at the battle of Jericho.' Good old Joshua didn't rest until 'they utterly destroyed all that was in the city, both man and woman, young and old, and ox, and sheep, and ass, with the edge of the sword' (Joshua 6: 21).

Yet again, theologians will protest, it didn't happen. Well, no — the story has it that the walls came tumbling down at the mere sound of men shouting and blowing horns, so indeed it didn't happen — but that is not the point. The point is that, whether true or not, the Bible is held up to us as the source of our morality. And the Bible story of Joshua's destruction of Jericho, and the invasion of the Promised Land in general, is morally indistinguishable from Hitler's invasion of Poland, or Saddam Hussein's massacres of the Kurds and the Marsh Arabs. The Bible may be an arresting and poetic work of fiction, but it is not the sort of book you should give your children to form their morals. As it happens, the story of Joshua in Jericho is the subject of an interesting experiment in child morality, to be discussed later in this chapter.

Do not think, by the way, that the God character in the story nursed any doubts or scruples about the massacres and genocides that accompanied the seizing of the Promised Land. On the contrary, his orders, for example in Deuteronomy 20, were ruthlessly explicit. He made a clear distinction between the people who lived in the land that was needed, and those who lived a long way away. The latter should be invited to surrender peacefully. If they refused, all the men were to be killed and the women carried off for breeding. In contrast to this relatively humane treatment, see what was in store for those tribes unfortunate enough to be already in residence in the promised Lebensraum: 'But of the cities of these people, which the Lord thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth: But thou shalt utterly destroy them; namely, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites and the Jebusites; as the Lord thy God hath commanded thee.'

Do those people who hold up the Bible as an inspiration to moral rectitude have the slightest notion of what is actually written in it? The following offences merit the death penalty, according to Leviticus 20: cursing your parents; committing adultery; making love to your stepmother or your daughter-in-law; homosexuality; marrying a woman and her daughter; bestiality (and, to add injury to insult, the unfortunate beast is to be killed too). You also get executed, of course, for working on the sabbath: the point is made again and again throughout the Old Testament. In Numbers 15, the children of Israel found a man in the wilderness gathering sticks on the forbidden day. They arrested him and then asked God what to do with him. As it turned out, God was in no mood for half-measures that day. 'And the Lord said unto Moses, The man shall surely be put to death: all the congregation shall stone him with stones without the camp. And all the congregation brought him without the camp, and stoned him with stones, and he died.' Did this harmless gatherer of firewood have a wife and children to grieve for him? Did he whimper with fear as the first stones flew, and scream with pain as the fusillade crashed into his head? What shocks me today about such stories is not that they really happened. They probably didn't. What makes my jaw drop is that people today should base their lives on such an appalling role model as Yahweh — and, even worse, that they should bossily try to force the same evil monster (whether fact or fiction) on the rest of us.

The political power of America's Ten Commandment tablet-toters is especially regrettable in that great republic whose constitution, after all, was drawn up by men of the Enlightenment in explicitly secular terms. If we took the Ten Commandments seriously, we would rank the worship of the wrong gods, and the making of graven images, as first and second among sins. Rather than condemn the unspeakable vandalism of the Taliban, who dynamited the 150-foot-high Bamiyan Buddhas in the mountains of Afghanistan, we would praise them for their righteous piety. What we think of as their vandalism was certainly motivated by sincere religious zeal. This is vividly attested by a truly bizarre story, which was the lead in the (London) Independent of 6 August 2005. Under the front-page headline, 'The destruction of Mecca', the Independent reported: