This is an issue that I've been on the fence with for years and I don't think I'll come to a good conclusion on it.
On one hand I strongly appreciate and enjoy the rights given to me to train my own assistance dog. It allows me to tweak tasks and my dog's training to best suit my personal needs and the needs of my disabilities. It is very empowering for me to be able to 'help myself' in this way and is a large part of maintaining my health at an acceptable level.
That said I don't think that the majority of PWD's are capable of training a dog to what I feel is an appropriate standard. It is very hard to be objective when you're independence and health will rely on your service dog and many people become blind to a dog's faults and don't wash them out when they really should.
I feel that program trained dogs are often not well tailored to a individuals particular disability, that they are highly over priced in many cases and that there is a huge feeling of "Program trained dog = safe or better" which allows many programs to fly under the radar and put out dogs that are ill trained and often dangerous.
The situation is little different when a PWD goes to a private trainer as the cost can quickly sky-rocket to the point where that person who is often of limited means can't afford a much needed aid for their own independence.
I have met badly trained dogs that were owner trained but I have also met badly trained dogs that were program trained. I think the law needs work, but I don't agree that it needs to take away the right to train your own dog, with the assistance of an outside opinion and help of a professional trainer it is a very viable option if you are able to be organized and structured enough to do the training.
I think there should be some higher standard of behavior set forth by the law and that service dogs should have to be certified... I'm not sure how this would work and who would over see it, or if it would become as difficult and paperwork heavy as Social Security currently is which wouldn't be conducive to a good system but something should be done to insure that dogs that are in public are not a safety hazard to themselves, their handlers, or the public.