Ezekiel 16:49 (New International Version): Now this was the sin of your sister Sodom: She and her daughters were arrogant, overfed and unconcerned; they did not help the poor and needy.
Comrade Will's homily: That's God speaking, so it's about as authoritative as the Bible gets. What are Sodom's first and most important sins? Being rich and not sharing. In the next verse, there's more: "They were haughty and did detestable things before me. Therefore I did away with them as you have seen." "Haughty" suggests Sodom's primary sins came from arrogance: its people thought they deserved to be rich while others were poor. As for the "detestable things" that are mentioned, see Genesis 19, where you'll find the only specific example: the mob tries to rape the newcomers. It's a powerful image showing how the rich try to take anything they want.