Many commentators have tried to justify the seemingly cruel act of God for genocide, methods of destruction, etc., especially in the Old Testament time. They tend to want to show mercy to those whom God has wiped from the face of the Earth by imagining the possibility that these could still be saved, and that the reason they are wiped away in the physical world is for their own good in the afterlife. I find it very disturbing when I recently came across similar interpretation by John Calvin on Uzzah's case in his 2nd Samuel sermons series. It seems as though if there is no slight chance of salvation for Sodomite souls or Uzzah, God would lack love.
I would rather say, that if none of these souls are saved, God is still the same just and merciful God. Thereby refuting the statement "for the good of these sinners so that they can be saved in spirit". I believe it is a irresponsible misuse of 1Corinthians 5:5, which has more instructive teaching value against the blasphemers than a mere excuse for the rest of us to live on our lives comfortably. However, if there's any lesson from all these, it is for the good of others, as an example for us to be mindful of and avoid, but I would never give a satisfying excuse to those who think God is cruel in doing so, and devoid them of appreciating God's immense grace to us who are no better than they and yet still alive today to have the chance to learn from the past.