There is a wrong approach to moral issues taken by some Christians that leads to a legalistic casuistry.
Casuistry is the attempt to apply general ethical and moral principles to particular cases of conscience and conduct. It is the effort to provide uniform, pat answers to every conceivable question of behavior. The casuist wants to have everything he can and cannot do in black and white, down to the smallest details of right and wrong.
There is nothing wrong and much that is right in wanting to understand how to apply biblical standards to specific life situation. We all need to be casuists in the good sense of understanding how to apply general biblical principles to the particular moral issue we face, but life isn't always as black and white as we would like.
Problems occur when we skip a step, when we rush to apply moral principles before we fully understand those principles. Instead of trying to identify in the Scriptures what the broad God-given purposes and functions of something He has created are (i.e. human sexuality, the Sabbath, etc.), we tend to focus our attention on the narrow question of which specific activities are permitted and which are not. We want to know what we can do before we have asked why we have this thing God has given to us.
This is the way Christians have been approaching important issues for centuries. "Let's skip the theoretical and theological and get right to the practical. I don't have time to study the themes and threads about this topic throughout the totality of Scripture. I just want a laminated wallet-sized list of do's and don'ts so I can get on with living."
That's the proverbial tail wagging the dog. Application must always be the servant of precept and principle. These logical shortcuts often lead to some kind of legalistic bondage or poorly considered licentiousness.
To think rightly, God's thoughts after Him, let's quit trying to insist there be a positive command for every behavioral choice we can make and instead learn to look at Scripture more holistically.
Adapted from Bruce A. Ray, Celebrating the Sabbath, P&R, 2000, p.10-12