Let's piss off NS again...I've been quiet for a while, but here goes.
There is no such thing as relative or subjective when it comes to evil and good.
What is good for one man might be evil for another, yes. But if there are no absolutes when it comes to evil and good, then there can never be a functional society.
Absolutes must be put into place in order for community to function, and for man to propagate.
If man's biological purpose is to reproduce, then we must be able to stand each other long enough to shag, give birth, and raise a child. If we all have different definitions of good and evil, then we must also have different definitions of sexy and non-sexy. Most of the time, we do not.
We agree that it is wrong to steal another's belongings, and in fact, we have a psychological disorder to label those who actually differ from this agreement. Antisocial disorder, look it up.
We agree that murder is wrong, that hate crimes are wrong, that war must have justifications.
However, based solely upon the merit that such things exist, and by observation of children without proper discipline, I personally believe that man is inherently evil.
Now, that does not mean we follow through with it. All (or at least like 98%) people have had at least one moment of anger or such similar emotion. What we do about it varies.
There is always a pacifistic or low-key solution to everything, but of course, some people choose not to utilize that, and thus screw it up for everyone else. Beginning a train of events that leads to hatred and evil.
Sparknotes:
Why is there evil? Because it can be defined. How was it defined? Because we all know what it means. How do we know that? Because we've all had moments like it at least once.