I think it depends upon the breed. Some have been bred for centuries to have their tail docked and as a previous poster stated injuries can occur and cause undue issues down the line. An example is Dobermans, their full tail is very brittle and can fracture and get injured very easily and then face infection and amputation latter in life. Some breeds still have viable tails, for instance the pembroke welsh corgi who's tail (when it appears - some still are born with a stub) is not as prone to injury. Many of the hunting breeds still should have them docked because they are worked in the field or as I stated above their tails are no longer viable long, the pem corgi on the other hand was docked for tax purposes.
I'll assume you are a responsible breeder and have gone the usually great lengths to bred the best to the best with all the needed health clearances and bloodline research and your breeding to improve the breed. If that is so, your breed standard calls for "
Tail is straight, docked or naturally bobbed, not to exceed four inches in length." If your breed standard calls for a docked tail then what are the chances of you getting the best homes for your puppies? Would someone wanting to compete in AKC events WANT a dog who does not meet breed standards? Is there a market for a tailed Aussies? Quite frankly as a 'responsible' breeder you should have done your research BEFORE your bred
I own a JRT who's tails are docked, they are still a working breed. I also at one time owned a rescued pem corgi and wanted another but after my research on the USA club's policies on docking have backed away, I wanted a pem with a tail, however, the best breeders will not do it because of the US club policies. I even took the time to talk with someone at the national level about limiting their gene pool because so many countries have banned docking and do they see in the forseable future a change in policy to have an either/or statute? They were soooo adamant against a change that it really turned me off. I have found several pem breeders who do not dock tails, however the quality of their lines are poor, they can not compete in the breed ring, many of the best bloodlines are closed to them and will not allow them to breed to their stock etc.
In the herding breeds the "theory" was the tail could be injured, but BC's, Cardigans and other long tailed working herding breeds have disproved that theroy. But in the hunting and working breeds there are some that have had injury while in the field.
Aussies, Pem Corgi's and Swedish Valhunds among others can naturally be born without a full tail and have a 'stub'. The SV's were recently admited to the AKC and smartly have written their breed standard to be all inclusive and not penalize dogs with tails, breeds that can have naturally occuring 'stubs' should all change their standards to be all inclusive, unfortunately many of these clubs are headed by people who refuse to see the other side.
Tail docking is a hot topic and their are many sides to it.
In the horse world drafts were always docked because it would get caught in the harness and do injury, now with improvements in equipment I'm finding some who are leaving the tail natural and when shown they just have to braid a bit more.
Many countries have banned tail docking on dogs all together, but I do wonder is it to the detrement of the breed? I would like to see the option of allowing a full tail in all breeds and then over time, breeders would work on improving things like brittle tails as most people in this day and age would prefer a 'natural' tail. Doing it this way would encourage quality breeders to work towards improving tail issues so that a 'natural' tail would not fracture and cause harm to the dog.
Also, people would get used to SEEING the breed with a full tail. One Standard Schnauzer breeder pointed out that if this breed is not groomed for what ever reason (they look completely different than any photo seen) and escapes they could easily be ID'd as a mutt but with the docked tail, rescue groups can ID the dog as a purebred dog.
I would like to see the US breed clubs work towards an either/or and as people want the natural look it becomes more a marketing issue and the breeders will work towards what the public wants and not ridgid breed standards. I know if I had my choice between a well bred pem corgi with a docked tail or natural tail I'd choose the with tail or natural stub.