To answer your question lets look at Jake Barnes, Robert Cohn, and Brett Ashley.
Jake is in Paris, unable to go home, after the war and his injury. Jake drinks, works, and yearns for Brett in a dizzying cycle. While Jake does not go out of his way to hurt anyone, he occasionally takes out his angst on Robert. Paris allows Jake to hide from the reality of his impotence through liquor.
Robert is also in hiding in Paris. He is hiding from his insecurities of his own manhood, his Jewishness, and his lack of character. He drinks, and tries to escape his own inadequacies, through adventures. His behavior is often bad, yet Paris allows him the freedom to escape his conscience.
Brett uses Paris to hide her miserableness in life through liquor and men. Paris also gives her the ability to delude herself into thinking if Jake had not been wounded, they would be together-and she would finally be happy.
All three use Paris as a way to escape the reality of their lives in the U.S.