While I will agree that certain breeds of small dogs are in "high demand", this does not mean that they should be bred because they are a certain breed. Below are some numbers pulled from today...
There are 1,769 Shih Tzu's or Shih Tzu mixes listed in Petfinder as looking for homes.
684 Bichon Frise
1,019 Boston Terrier
2,427 JRTs and 633 PRTs
708 Lhasa Apso
With this many "high demand" dogs currently seeking homes in rescues listed on Petfinder (not to mention all those that are not listed on there!), I don't see that there is too high a demand not being filled. What I do see is that people are too lazy to look for a dog - it's easier just to get their dog from the breeder up the road, right? Of those listed, there are a fair amount that are purebred. There are also a fair amount that are puppies. Yes, many are adult or older dogs, but that is not the whole of it.
Also, if searching for a dog of a specific breed, why not contact a breed-specific rescue? They are not all listed on Petfinder.
Regardless of the breed of dog and whether or not it is in demand as a pet, I still believe there are certain accomplishments that any dog bred should reach before breeding.
I don't believe that dogs should be mixed on purpose since there are so many people who have Oops's in their backyards. That said, IF you DO choose to mix two breeds together, both parents should be registered with a LEGIT registry (I'm thinking AKC or CKC here people) and they should also have something to their name in an accomplishment. Did they win a show? Did they achieve a certain level of Obedience Trials and recieve a prize or acknowledgement? Did they earn a certain level of herding or ... SOMETHING!
I don't believe dogs should be bred without reaching some level of potential and I don't believe that untrained dogs should be bred.
I think that puppy mills should be illegal in all provinces and states and animal control (or Animal Protection Services through SPCAs) should have the ability to charge the people running them. Not only that, I think that they should be charged with hoarding. Maybe give them a fine for every dog that doesn't have a dog license??
I hope I've explained my opinion well enough? Is this so?