1 Corinthians 6:12

All things are lawful unto me, but all things are not expedient: all things are lawful for me, but I will not be brought under the power of any (KJV)

Then: "They say, I say; They say, I say." That's the counterargument diatribe Paul uses to side track Corinthian objections to his denunciations. He discards their excuses even before they can say "There's no problem with our sexual actions" (Baker, p. 92). The phrase that "all things are lawful" probably comes from a sentiment that they were forgiven in Christ and now free to do anything they wanted. Fee (p. 251) describes it as a slogan specific to the Corinthian Church. They may have misunderstood Paul's earlier teachings about motives and actions. If there is nothing unclean about an item or action alone, food for instance, then they thought they were free to do as they willed in spite of its effect, or for that matter, any of the teachings of Christ. The Corinthians got the non-essential choices of daily life mixed up with theological choices about ethics.

Now: We get mixed up in the same ways. We might focus on tatoos or body piercing or botox treatments -or even be into the same kinds of sexual problems of verse 9 (fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind) rather than the ethical principles of any action's outcomes. How do we escape? First study the difference between "lawful" and "expedient" (beneficial) and "lawful" and abandonment of God-centered self-control. Conviction first, behaviors second.

Extra sources: Cornerstone Biblical Commentary 1Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.
The First Epistle to the Corinthians by Gordon D. Fee (Eerdman's 1987) online at http://books.google.com/books?id=XlBp10nUTXAC&dq=Gordon+Fee+Bible+commentator&printsec=frontcover&source=in&hl=en&ei=SwLNSu3nA4v6Mf2XlDo&sa=X&oi=book_result&ct=result&resnum=12#v=onepage&q=&f=false