Fun fact: originally the docking of tails on breeds suck as Dobermans and rottweiler's and Pitbull's were for an actual reason as they were used as working dogs and it was for their safety because in their original job's tails would be severely injured or amputated due to said jobs. But nowadays its only done out of vanity from the owners. There isn't any real reason to continue.
Also, this is done when they are still very young pups. and anyone that that complains and say its cruelty to the dogs should also agree that doctors should also stop giving males circumcisions when they are babies. pretty much same principle.