Jamieson, Fausset and Brown on 1 Corinthians 5:10

10. Limitation of the prohibition alluded to in 1Co 5:9. As in dissolute Corinth to "company with no fornicators," &c., would be almost to company with none in the (unbelieving) world; ye need not utterly ("altogether") forego intercourse with fornicators, &c., of the unbelieving world (compare 1Co 10:27; Joh 17:15; 1Jo 5:18, 19). As "fornicators" sin against themselves, so "extortioners" against their neighbors, and "idolaters" against God. The attempt to get "out of the world," in violation of God's will that believers should remain in it but keep themselves from its evil, led to monasticism and its consequent evils.