What makes you think that good and evil are just a myth? Just because they've both existed for hundreds of thousands of years? What are you even trying to prove? That spilling the guts of innocents and reveling in it is somehow good?

For me personally, answering what evil is is more difficult than answering what good is. Because evil is far more insidious; unlike good, it's capable of disguising itself. I've encountered people who pretended to be my friends and betrayed me as soon as I was no longer useful to them. From a young age, I was extremely naive and trusted these people, almost like brothers. So, evil is a murderer disguised as a monk. In our time, it's the most common type.