Absence of good might be the starting point but Dahmer killing and eating other people was not simply an "absence of good".I tend to agree and Augustine uses this line of thinking in his logical deconstruction of "evil"; however, these religions hold the evil is real, not nominal, and absolute. For these religions, it is not simply an absence, it is its own force.
However, "evil" is not "its own". It is the "actions" of a free moral agent acting against "good" or more specifically acting in the absence of "God".