A Christian should always display fruits of the Spirit not of the flesh. Things like forgiveness instead of revenge, helping one that is down instead of kicking them when they are down are those things that indentify a Christian a separate person. This is what will give the Christian a strong witness. We must do things to maintain our spiritual strength and our witness. Just as with our physical strength there are things that help and detract from our spritual strength.
Sin sears the conscience, the first time a sin is performed is always the hardest.
After that is gets easier each time as our concience is hardened. Our society is such that many forms of sin - especially habitualy types are actually considered acceptable. Even if you do not actually participate in the sin, you are still exposed and allowing you conscience to be hardened. No man, having put his hand to the plow, and looking back, is fit for the kingdom of God. Looking back here is looking back at the life the man left.