Thanks for your post, Hazel.
It is people like you who are not afraid to resign over the mistreatment of animals, and not afraid to speak out publically, who will help make a difference within the SPCA. The SPCA counts on the huge majority of people slinking away in silence, or hanging on with their eyes closed, and their mouths zippered up in the hopes that they can make a change for a few animals. But they can't really make a change if they allow these atrocities to continue.
The arbitrariness of these killings infuriates me. Dogs that volunteers are allowed to walk and socialize, and dogs that are publically listed as adoptable are then killed in the space of a few days. This makes no sense.
It also upsets me that the SPCA allows the volunteer dog walkers to "train" the dogs, without the volunteers first having training themselves, and then supervision for some period of time. It's been my experience through observation that many people, including serious dog-lovers, do not have the knack for clear, consistent, effective dog-training. (Which is not to say that it can't be learned.) People often just aren't attentive enough to the dogs, and the click, or reward, or praise, doesn't come at just the right time. So to let various untrained people all have a go at training the dogs is at best probably not all that useful, and confusing to the dogs - best to just walk them and give them lots of love.
By the way, I am a dog walker at a boarding kennel, and many dogs show serious aggression aimed at the dogs who are walking by their pens - and they are dogs with no aggression problems at all when they are not caged, stressed, bored, frightened, or whatever else. If anyone decides that a dog has to be killed for aggression based solely on their behaviour while kenneled, with other dogs walking by, then that person needs a desk job, and not in a facility that deals with animals.