The book of Genesis (in chapters 13-14 and 18-19) tells us about the evil city of Sodom.
First we read how Lot, Abraham's nephew, settled in Sodom despite the fact that its inhabitants were "very evil and sinful to G‑d." Sodom is ravaged by Cherdolaomer's armies, and Abraham comes to the rescue of his captured nephew. Then we find Abraham pleading with G‑d to spare the sinful city in the merit of the righteous residents that may be there, but it turns out that not even ten such persons can be found. Two angels, disguised as men, visit the city, but only Lot will offer them hospitality. Lot saves them from the Sodomite mob, and they, in turn, rescue him and his two daughters before destroying the city.
What were the sins of Sodom? In the English language, the name of the city is synonymous with sexual perversion. This derives from the Torah's account of how the mob surrounding Lot's house demanded that he hand over his two guests to them "that we may rape them." But the traditional Jewish sources -- the Talmud, Midrashim and the Commentaries -- have a different angle on the Sodom story. There, the emphasis is not on their sexual sins, but on their lack of hospitality and their virulent opposition to anyone who dared share any of the city's wealth with a stranger.
In the words of the Talmud: "The men of Sodom were corrupted only on account of the good which G‑d had lavished upon them... They said: Since there comes forth bread out of our earth, and it has the dust of gold, why should we suffer wayfarers, who come to us only to deplete our wealth? Come, let us abolish the practice of lodging travelers in our land..."
They even found a way to be charitable while ensuring that no stranger would benefit from their charity: "If a poor man happened to come there, every resident gave him a dinar, upon which he wrote his name, but no bread was sold to him. When he died, each came and took back his dinar." They went so far as to decree: "Whoever hands a piece of bread to a pauper or stranger shall be burned at the stake."
The story of Sodom appears in the Torah against the background of Abraham's life. Indeed, Sodom is the antithesis of Abraham, who is portrayed by the Torah as the very personification of chessed (benevolence). Abraham gives of himself, materially (providing food and lodgings to wayfarers) and spiritually (sharing the truths he discovered, praying for Sodom); the Sodomite is intent on keeping for himself what is his.
What's notable about the people of Sodom is that they are not thieves (as was the generation of the Flood). Even when they deprive an interloper of his possessions, they are careful to do it in a "legal" manner. In fact, their basic philosophy seems quite benign. In the words of the Ethics of the Fathers:
One who says, "What is mine is mine and what is yours is yours" -- this is the trait of Sodom.
What can be more fair? Granted, the people of Sodom took this to quite repulsive extremes. But is every person who declares "What is mine is mine and what is yours is yours" a Sodomite? All he's saying is, "I won't touch what is yours, but don't expect me to give you anything."
To the Jew, such fairness is the essence of evil.