I feel rather strongly on the topic as well, so long post. I'm coming from a dog perspective here, but it applies to other animals as well, I think. I truly think that unless you plan on showing a dog, or using a dog for a breed-specific job (like for birding or herding), people should investigate shelter/abandoned/rescued animals first.
I got my mother a dog from the shelter 7 years ago, who just was put down a week ago today because of a stroke ((sniff, sniff, we're all still very emotional about it)). San Francisco has a no-kill policy, so Ubu (formerly named Ella, 2 year old shepard/dobbie/lab mix) had been in the shelter for two months before I found her. She had been a bit traumatized, and would not bark or come to the door. I ended up selecting her over a yellow "almost pure" lab youngster that had just shown up at the shelter. Because my mother was single, with no children at home, Ubu was the perfect companion to my mother for these past 7 years and blossomed under her care.
My own dog, Rambler, an APBT/Shar Pei (Pit Pei) mix, was "purchased" as a rescue from a neighbor at 6 weeks old. Without my influence, Rambler would have probably been given to a pseudo-macho guy who wanted her to breed or fight. Now she's a 55-pound lap dog who think she's a cat, loved by my mother and grandmother.
These are just two examples of how adopting or rescuing can provide new life for dogs that would be in dire straits. There are many pure bred dogs that you can still rescue (my neighbor has a wonderful (and best friend of my dog) pure Rottweiler that had been used to breed two litters first). I'm not completely against purchasing pure-breeds, but I think some folks like to have the "name recognition" that comes from a pure-bred rather than a respect and appreciation for the breed itself.
Last note, just want to point out for all the predictions you can make from a pure-bred from a behavioral standpoint, you also get a host of medical issues that you don't get from a mixed-breed. Many people not familiar with the chronic health conditions from a Shar Pei, Pug, or Dalmatian are unpleasantly surprised and frustrated when they're encountered.
By the way, I love pure-bred papered black Labs and now have a love for pure-bred papered APBTs as well!
