I do want to speak up for responsible breeders. There is a reason many people like specific breed or breeds of dogs. Just go to a all breed dog show and you realize that there are folks that worship and love each of these very different breeds and they can tell you the pluses and minuses of their beloved breed. Believe me there are many that I could not see living in my home. Individual dogs still have their unique qualities and personalities but most breeds still have some general characteristics that have come from years of being breed for a specific purpose. Prospective owners need to research each breed and not be surprised to find out that their "terrier" is a little head strong. Or that their Border Collie has so much energy and keeps circling the children and nipping their ankles.....
Some breeds do have some specific health issues due to the extreme focus on a specific breed quality....(I am thinking of the extreme shortening of the noses that then effect ability to breath, hind legs and hips on American GSD or the back problems with some of the long backed breeds....) But pure breed dogs do not necessarily have more health problems than a mix breed....it is just that what health issues there are have been tracked and recorded. Not so many specific statistics follow the all American around.
I know that in English Cockers there have been several conditions that have shown up but because there has also been extensive studies and research in the breeds there are now tests we can use to help both pure breed and mixed breed dogs.
Anyway I will get off the soap box....but for anyone I recommend research on breed type and asking lots of questions whether you decide on a mix breed or a pure bred. Most all of us earn to love the one we are with but it helps to aim in the right direction whe it comes to temperaments and talents to begin with. Few people confuse living with a poodle with a living with a Golden with living with a terrier....