While I am very pro-adoption, I know that for some people, adopting is just not practical and/or effective. Mutts are great, but there is a reason there are so many different breeds out there - because people want different traits/personalities/etc. in their pet. If all dogs were mutts, they'd evolve into the same dog (this happens in areas with large feral/wild dog colonies - after multiple generations, the dogs start to lose the breed-specific features).
However you obtain your dog, do your research and don't promote bad breeding. Don't buy a dog from the guy down the street who lets his female dog get pregnant whenever he needs extra money; don't buy from the couple who think their dog is so perfect that they "just had to breed him", etc. Buy from the reputable breeder.