*researches*
I was pretty much right with the 'violence' thing.
Sodom and Gomorra were basically bastards to everyone around them. They 'raped' everything near them and abused the hell out of all their neighbours. So when Lot had two angels staying in his home a bunch of guys came to the house and were all "We wanna rape the visitors". So the Angels were all "Haha. **** you" blinded everyone and destroyed the city.
Most people interpret this as an anti-homo story, but 'rape' is used in the 'rape and pillage' sense meaning they wanted to screw them over and take their stuff.
So while God was pissed at the general stench of sin coming from the cities, when he finally got around to laying waste to them it was because every last man, woman and child in the cities was so corrupt, violent and generally sinful that he just couldn't ignore it anymore.
Or condensed: It wasn't just the massive amount of sinful sex going on, it was everything about the two cities that caused God to smite them. After all the crap that got up to Heaven about the cummings and goings in Sodom and Gomorra, God decided he needed some accurate reports on what the hell was happening. He found that everyone deserved to die, so he killed them.
One-liner: They were burned to death for being bastards.
