The need to destroy the cities of Sodom and Amora, requires investigation. There were many nations that committed atrocities, but we never heard of them being utterly erased from the face of the earth.
The Torah gives us an explanation as to what caused them to be deserving of such a fate. We are told that the people of Sodom were רעים וחטאים מאוד. They were exceedingly sinful and evil.
Their evil was so great that they were unable to show compassion to other human beings. Their fate was sealed when they were unable to feel the pain of the poor.
There is also an opinion that the cause of their demise was the lack of any kind of justice system. Their judges were corrupt and never executed true justice. We are told that the guarantee for our being able to inherit the land, is to have judges who become partners with Hashem. They fear Him and will act diligently to enforce the laws of the Torah.
It is often hard to believe when one meets people who have corrupted their ways to such a low level. They lie incessantly and are completely self absorbed, only seeking personal self gratification. They act cruelly and do not care who they might trample upon.
Unfortunately, such people exist in our society. Imagine an entire city where this is the way everyone acts. Hashem explained to Avraham that He had no choice because the cry of their evil had reached the heavens.
Man has so much potential. If he applies himself, he is capable of reaching the level of angels. If he allows himself to fall, he can sink to a level lower than the animals.
The story of Sodom and Amora is meant to make an impression on us. We must work hard to reach our full potential. We must become more kind and more compassionate. We must feel the pain of others. This is how we grow and create a positive and meaningful as taught by our great sages and the Torah.