OK, I understand your argument, but I think it's based on incorrect assumptions. This is the way I see it: There are a number of people who will always buy dogs and will then get rid of them or have them put down for a number of reasons. There is already a market for these people, and there always will be. People like me who would not put a dog down (unless to prevent suffering) and would not send it to a rescue centre, do not increase or decrease this number of people, or the cost of dogs by buying dogs from breeders. We increase the number of dogs, but not their ownership by irresponsible owners. I'd like to draw a venn diagram to describe this better.
I agree that by buying a dog and not rehoming one, I would not be part of the solution. But neither would I be part of the problem. As it happens, I did rehouse one.
I don't think we're arguing about whether it's learnt, memory-based or otherwise (at least I'm not). The fact is previous experiences affect a dog's behaviour. Why would someone want a dog that they had to then take through these forms of therapy, when they can get one from a reputable breeder with whom (more often than not) they would not.
Also, it's not as simple as giving your dog a biscuit for a few months when they see something they're scared of. As you well know, some dogs take many years to get over certain phobias (or whatever you would call them), or never fully do. I have some friends who have a lovely rescue dog who is scared of men - for very good and quite harrowing reasons. They've been to a number of dog professionals and are following the best advice to the letter. The dog is still scared of her male owner (albeit slightly less so).