Some interesting thoughts from Carl Trueman:
I wonder if there is a more neglected text in the New Testament in the current revival of interest in reformed theology than Eph. 5:12? In the reaction to the taboos of old-style fundamentalism, there is surely a danger that we have lost all sense of what is biblically appropriate when it comes to engaging the wider world. I had my own first-hand experience of this a few years ago when I suggested on this blog that it was perhaps not appropriate for Christians to see the film Milk which was not only a highly fictionalized account of the life of Harvey Milk but also included, according to the reviews, sexual scenes of an explicit and inappropriate nature. I still remember the teacup sized storm of protest as various Christian culture vultures treated me to lectures on how my narrow mindedness was not going to stop them using Milk as a means of witnessing to friends. But none of the outraged evangelists addressed Eph. 5:12.
More recently, the very public preoccupation in the evangelical world with what are apparently pretty explicit treatments of the subject of sex has brought to my mind Eph. 5:12 once again. Paul, of course, was no legalist. He affirmed free grace and Christian liberty. Yet he wrote Eph. 5:12. So what does it mean? Well, it actually means exactly what it appears to mean. You really do not need a postdoctoral qualification in Second Temple Judaism to crack this one...
...I have often in the past stood with those who laughed at what we regarded as the ignorant, unsophisticated taboos of the older generation. But now I worry about the ease with which the rising generation talks explicitly of 'the fruitless deeds of darkness' in the name of cultural engagement, fear of being thought passé or simply a desire to slough off the legalisms of their fathers in the faith. You can, after all, get to heaven without ever having seen an R-Rated art house movie or having enjoyed a spectacular love life.
Here's a question: would it make any difference to you, any difference at all to the way you talk, to what you watch, to the way you "engage culture", if Eph. 5:12 had never been written?