We know it when we see it. We don't have to believe in Evil, it loves to rear its beautiful head. I say that based on the Judaeo-C take on Satan being a Pretty mother****er.
As for evil, it certainly exists and something assists its continuity, even if its the apathy on our part to annihilate it. Does absolute Good exist? I wonder why we avoid asking that? We may not, since so many people believe that God exists, that He is extremely good, if not exceedingly good, and therefore --- Absolute Good. Sounds like the kind of Drink for me on a Friday. "Absolut Good."
I think its just another extension of Metaphysical, A Priori value judgments, vs A Posteriori. It's where some thinkers deeply and passionately want to go in their hearts and minds, and where other's fear treading because they genuinely fear that making a discernment might be confused with them passing judgment.
Does it exist? A matter of A Priori thinking.
Can we put it under a microscope? We would not ask such questions as does Absolute Good or Evil exist if we could.
If we could, neither of them would allow it to take place. Evil would see to it that we remain sheep for its food and fun, and Good would see to it that we remain sheep so that when we behave good or morally, we don't do it out of compulsion, but out of a genuine love for good needing to be done for the closest thing to peace on earth's sake.
If we could see either one, then we'd know that both are Facts. That we cannot, is a matter of relativistic modern thinking, and therefore, a matter of what we believe and regard as being True.
Yes, absolute evil exists, but I don't want to see it to know because it is exceedingly beautiful and I may just fall in love with it lest something keep it at bay from demonstrating what it could potentially do for me. I am safe in making that statement as are all of us who wish to discern black from white - the Absolute, and the Good.