It's not only considered cruel to dock tails but also makes no sense to take away the dogs comminucation.
i couldnt find any written information about it but, what i am told is because of their strong tails rottweilers are used in water search and rescue and they are excellent at it.
My rottweilers tail was docked when i got her. When i see her waving her butt instead of her tail it breaks my heart.
My bullie is not docked and i can read his body language better that the rottie.
Ear chopping and tail docking is forbidden in Turkey. I see dobermanns with tails and "normal" ears, they seem funny because i am not used to seeing them without chopped ears, i see rotties with tails it gives them a more noble look and they carry it with such pride as if saying "i am the king of the world" (which sure they are)