So I ask instead: Is it possible that you could ever be wrong about your determination of something's good or evil nature?
So based on my example above, yes.
Phew! My whole argument was about to go down the tubes!
Actually, you've jumped ahead quickly enough that I think I can dispense with the plan I was going to take. Battle plans, contact with enemy, and all that.
Let me refer to your example of how you learned to adjust your conduct towards your wife. You said:
I was doing something evil even though I did not interpret it that way. Finally I realized what I was doing and stopped.
Would you say that you learned something, something positive from this? (I'm just being didactic, don't worry) Of course you did. You learned something very important about yourself -- namely that you possessed an ability to be inconsiderate even about someone who means so much to you. Once you realised this you were able to stop behaving in such a manner.
I suggest that this is a positive result. This is a benefit. A benefit gained from performing an evil action. So clearly there is benefit to be found in the performing of evil actions. You have found benefit yourself. You are a better person because of the actions you performed.
You might say, no, I am a better person because of my own honesty and integrity which enabled me to observe my conduct clearly. I say that without the conduct to observe in the first place, all the honesty and integrity in the world serves no purpose. The clear fact is that you performed an evil action and as a result you are a better person.
This is exactly the sort of thing I have been trying to put into words all along. What we see here is exploration at work. You acted in a manner you did not see as evil. Let us say that you explored a path that did not have a big "EVIL" sign over the entrance. As you travelled down that path, however, you came to realise that it was in fact a path to evil. As you did so, you learned important things about yourself and people in general.
This is what I mean when I say that sometimes we don't know that we are exploring evil until we have done some exploration.
This means that sometimes we will necessarily explore evil.
There's a further corollary to this, which is that our knowledge of evil is constantly growing, as we try out certain paths and reject them when we discover they, too, are evil. This means that not all of us can possibly possess the same degree of knowledge of good and evil at all times.
The path of sarcasm to one's wife, for example, is clearly evil to you. It may not be so to me, and perhaps the only way I can learn is by travelling that path just as you did. If this is true in this case, it is true in all cases. This is NOT moral relativism. We still apply our perfect and true moral standards to whatever we discover, assuming we possess such.
Now to you it may seem clear that exploring the path of "writing CE in the box labelled Alignment" is evil. But to others it may not, and indeed, for them it may turn out to provide them with all sorts of benefits. You have no way of predicting that. What benefits one of us may not benefit another -- we never get the same results from travelling similar paths. My point is that there is no way to infallibly predict the result of ANY given path.
I repeat, this is NOT moral relativism. We can still apply as perfect a set of standards as we can find. We just need to know to what we are applying them. And we can suggest that certain paths are very likely to produce few if any benefits, if we have the evidence to back them up.
The point is we can say without hesitation (I suppose) that murder is evil. The problem comes in trying to define a particular case as murder or not. So yeah, we can say that murder provides no benefits (though speedy inheritance comes to mind), but that doesn't always help the individual trying to decide if THIS particular case is actually a murder or a justifiable homicide, and therefore presents a path they should be following.
What I believe I've just proven is that there is no way to say that playing evil characters provides no benefit. Correct me if you think otherwise.