Why does Paul pay special attention to the sexually immoral in 1 Corinthians 5:9-11? 1 Corinthians 5:9-11 states that


  I have written you in my letter no to associate with sexually immoral people -- not at all meaning the people of this world who are immoral, or the greedy and swindlers, or idolaters. In that case you would have to leave this world. But I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat.


Why are the sexually immoral singled out as those with whom the Corinthians should not associate? I don't see any reason why such sin should be considered better or worse than any other. Thank you.
Because, as 1 Corinthians 6:18 says,


  Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body


As a port-town frequented by sailors (and Cretens!) Corinth had a lot of sexual sin going on. The town had all sorts of temple prostitutes.  In sinning with said prostitutes, a person is using his own body in such a way as to bring disgrace to Christ:


  Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, “The two will become one flesh.” 17 But whoever is united with the Lord is one with him in spirit.


And finally, at least one member of the Corinthian church was engaging in gross immorality, even by the standards of such an immoral town.  As 1 Corinthians 5:1 states:


  It is actually reported that there is immorality among you, and immorality of such a kind as does not exist even among the Gentiles, that someone has his father’s wife.