“Temporary deviations from fundamental principles are always more or less dangerous. When the first pretext fails, those who become interested in prolonging the evil will rarely be at a loss for other pretexts.” James Madison, 4th president of the United States.

This applies to compromise in the face of temptation. Once a person opens the door for self-justification or excuse, there is no stopping the slide. That is because each succeeding rationale proves easier, for it follows right on the tail of the previous one. The weakness that smoothes the pass to cross the line one time, is the same weakness that crosses the line next time. We might as well face and conquer the first temptation in our heart, which will then strengthen us for that temptation each time. 

But each one is tempted when he is carried away and enticed by his own lust. Then when lust has conceived, it gives birth to sin; and when sin is accomplished, it brings forth death. (James 1:14–15)