There are a lot of pure breed dogs in shelters too. Just check out
www.petfinder.com and see for yourself.
If we all really want to help shelter dogs get homes, then we shouldn't even buy a pure bred dog from a breeder. Every pure bred dog that is bought from a breeder is taking a home away from one shelter dog -- this obviously applies to mixed breeds too.
I personally bought my 2 dogs from a breeder. But in the future, I plan on adopting one from a shelter.