This is a tricky one.
Since good and evil are truly relative and perceptive terms, I find it very hard to believe that there is a true, absolute good and a true, absolute evil. Where one group might see something as good, others might see it as evil. This creates more tension, in my opinion, than any debate over the existence of God or the Devil. Actually, I think that this opinionated conflict is either unknown or unmentioned, and is the very root of the 'greater power' arguments.
That isn't to say that I don't believe in anything; I do believe in God, just not in the manner in which he is portrayed so widely. my beliefs of the relativity of good and evil disproves the Christian teachings to me because the Christian faith, and the Catholic Church in particular, have done many a foul deed in the past under the pretense of justice or divine providence. The Crusades, for instance, were a mass slaughter of innocents under the gist of "because their holy stuff should be OUR holy stuff," and those that fought back were branded as evil, sacrilegious heretics who were either hunted and killed or exiled. One can preach "this is good, this is bad," but when they contradict themselves and do that bad and say it's good, they fall victim to the egotism of the true believer; that one can do no wrong if he or she is willed to do it by God or is repentant of his or her predefined sins.
The ego comes into play when a particular belief, however humble or true in its message, is contradicted by the actions of its followers. Those who will abuse the standing and power of a long-rooted faith will often justify themselves with the beliefs they are slowly killing. It's being able to get away with anything, and play the "it's God's Will" card or the "the Devil made me do it!" card. Either way, the original meaning(s) of the religion or belief are screwed over because of the egos of a few pious assholes.