Because you didn’t understand the underlying messages of the books.
I have learned that there are good people who simply lack imagination and the ability to be transported by literature, song and art into a different reality then the one they currently occupy. Frequently, but not always, faith in God is difficult for these people as well. Perhaps it is genetic, perhaps those with imagination possess a gift. I don’t know, but I do know it inspires greatness.
Gollum is completely destroyed by the ring, more than any other character in the series, and ultimately He destroys the ring and himself saving middle earth. Without Sam and Frodo’s mercy toward him in the journey toward Mordor Middle Earth would have fallen to Sauron because Frodo did not have the strength to resist the power of the ring. The victory over evil relies on mercy toward all of us as we are all broken and unable to resist the temptations of sin.