I don't remember this story being this brutal when I first read it as a kid, though that might be because I was extremely ecstatic, as all kids were, to be reading a story in which the main character is a dog. My fetus brain was like: YAAY, DOGGO GO BRRRRRRR!!!
Now that I have read it again, I am happy to report that I might have found a reason why this book is a classic. As a kid, you read this story for a dog. Then, you grow up. The years go by, and the more time passes, the more you miss your childhood. You could do a lot of things to try and recreate the atmosphere and the feelings from parts of your childhood and you simply choose to go back to the doggo story. There awaits you nothing of your childhood and you are tricked into pondering over the question of violence as a tool!
There goes a part of my childhood, yet it was not completely lost. It has morphed into something else, perhaps just as valuable.