In politics, a district is said to be "gerrymandered" if the people drawing the district lines have made improbable twists and turns solely to favor their own position and give an outcome more favorable to their own partisan interests. Generally, there is no identifiable reason for the final results other than the electoral advantage they give to the persons who are using their legal authority to give themselves an advantage -- and to put their opponents at a disadvantage.
The same effect takes place in morality. Often, "right" and "wrong" are gerrymandered in favor of each person's perspective. "Right" -- what is "in bounds" -- may mean nothing more than "the set of goals or virtues I am pursuing"; "wrong" may mean nothing more than "the things that really bother me, or that my opponents do" -- those are out of bounds. The problem, again, is that it's self-serving and partisan. (Can anything like that possibly be genuinely moral?) It is a truly rare situation in which all the good is on one side. More typical is that each side has gerrymandered "good" and "evil".
The original "gerrymander" -- the one that inspired the name, looked a little like a salamander. When we gerrymander good and evil, what does the picture look like? The lines we draw for "good" are typically a flattering self-portrait, and our picture of "evil" becomes a caricature of our enemies -- often a malicious one.
And in that fatal move, morality loses all its power to transform us, to guide us, to heal us, or to inspire us. It loses its power to win over our opponents. Gerrymandered morality is impotent. Morality can only transform us when it is an image that is better than we are -- that is, the image of God.