Paul must correct the church because of gluttony, drunkenness and going to prostitutes at private banquets (6:12-20). The issue here is attendance at banquets given by the rich elite of the city. There is plenty of evidence concerning the types of things that went on in a Roman banquet of the first century from contemporary writers.
Winter gathers a number of references from Plutarch describing the combination of gluttony, drunkenness and sexual immorality that were a part of the “after-dinners” as he calls them. There was an association between gluttony and sexual excess, as is seen from the well known saying reported by Plutarch, “in well-gorged-bodies love (passions) reside.” The writer Athenaeus said that the goddess Cypris (Aphrodite) does not visit the poor, “in an empty body no love of the beautiful can reside.” Plutarch also said that in “intemperate intercourse follows a lawless meal, inharmonious music follows a shameless debauch” (Winter, After Paul Left Corinth, 84).
These banquets would only have been attended by the rich elite of the city of Corinth. The poor were not invited, only those of some social standing. In Corinth there was a major city-wide banquet for all citizens celebrating the games. Not only would there have been pressure to attend these banquets on a social level, there was the added pressure of begin a good citizen of Corinth and of Rome
Why would the Corinthian Christians think that they had a right to participate in these banquets? Paul seems to have taught them that Christians are to be separate from such activities, and the strong Jewish ethic of many of the founders would have argued against going to a temple, eating food sacrificed to idols, and participating in the “after-dinners.”
It appears at the very least that the Gentile converts to Christianity did not see this activity as sin. As with most of the problems Paul treats in 1 Corinthians, the congregation is slow to de-paganize. The practice of going to temples to share meals with the elite of Corinth was socially desirable for the wealthy and “wanna-be” elite. Perhaps individuals in the church thought they had to do their civic duty by doing to the banquets (a virtue) and did not yet see the additional practices as a vice yet.
While it is easy to point at the Corinthians and judge them as “immature,” it seems to me that the church in general as well as individual believers are quick to compromise with “the world” when money is involved. Sin is condemned with the poor people are doing it, but if a wealthy member of the congregation is involved, the condemnation is quite a bit less severe. A church might borrow a practice from the corporate business world because it “works” without really thinking about the origins or ramifications of the practice. I can think of a hundred great excuses for behaving any way I please as a Christian, most of them are well-intentioned. I suspect Paul would have an equally strong condemnation for the modern church as he did Corinth!