Why is Grendel portrayed as being sympathetic?

The poet/author wanted to tell 2 sides of the story. If you read the book, "Grendel" you will understand why he was made into what he is. Since Grendel is a descendant of Cain, the moment he was born, he was in the eyes of other just as evil as Cain. But his mom wanted to protect him from the ugly world outside. Grendel was made like this by those humans who pushed him. So that can show no one was born evil and can refer to situations in today's world.