Trivializing both the Gospel and the Creation
Or consider the arts. Because we know that the ability to draw and paint, write and sing all belong to the goodness of God's creation, we are able to fully participate in the arts. No one should enjoy a good book, painting, or symphony like a Christian.
We can enjoy every good form of artistic expression-- including bluegrass!-- even when the art is not making a distinctively Christian point. It's wonderful to use the arts to creatively spread the gospel. But the point is that even when they do not, even when a piece of art is "secular," we may still enjoy it as a vital piece of God's good creation.
I am not encouraging participation in sinful forms of artistic expression. The fall has extensively damaged creation, and in few places is it more evident than in the arts. Certainly we should avoid any music, movie, or visual art that stirs up sin, such as pride and lust. My point is only that we don't need to stamp Christianity on something before we can enjoy it. In fact, our feeble attempts at baptizing creation tend to cheapen both it and the gospel.
Putting "cross-training" or "cross-eyed" on a T-shirt trivializes both the cross (do we really want to compare Jesus' suffering to a type of exercise or astigmatism?) and ordinary T-shirts (which are perhaps not as good as those with religious slogans). The same holds true for spill-proof cups emblazoned with John 4:14--"whoever drinks the water I give him will never thirst"; key chains that parody milk advertisements with the probing question "Got Jesus?"; dinner plates that claim to be "Home Grown and Heaven Bound"; and stuffed ducks wearing rain gear on account of recurring "Showers of Blessing" (honestly, I could not make this stuff up). Rather than improve creation, such silliness only distracts from the goodness that is already there, while mocking the gospel it seeks to advertise.
Michael Wittmer, Heaven Is A Place On Earth, pp. 66-67