So listen, young people. They are the swingers who live together unmarried, the wife-swappers, the prostitute patrons, the kids at school who twitter about their weekend connections. The push for free sex was there long before we had any puritanical or victorian ethic to rebel against. They were saying that what we do with our bodies does not matter and in fact the more sensuality you pursue, the more you show your true Christian freedom from the law. In the name of grace and in the name of Christ they perverted Christian moral teaching and in that way denied the Master who bought them.
All immorality is just as old-fashioned as Biblical morality.
It is enslaved to irrational passions. And unless it turns and repents it is doomed. That's what the rest of our text is about. The point of verses 4-10 is to warn us that since God has punished unrighteousness in the past he will punish it in the future. Peter illustrates God's wrath with three cases in verses 4-8 and then draws his conclusion in verses 9 and 10.