The concept of purebred dogs is not a bad one; it’s just the state of many purebred dogs (and other animals) is awful right now.
Theoretically, having a purebred dog would be a way of determining size, looks, and approximate temperament of the animal you are hoping to get. And that is generally a good thing; some owners live in apartments and some live on farms, some want working dogs and some want lapdogs. It’s good for both the owner and the animal if they match up.
Where breeding can go wrong is when the looks and price of an animal matter more than the quality of life that its genes will cause it to have.
The two main issues affecting purebred animals can be summarized to inbreeding depression and overbreeding, both of which I’ll discuss in detail (and with science) below.
This is why it’s so so so very important do your research before adopting a pure breed! Not just their breeder history but the breed itself! Are you adopting a specific breed purely for looks or because you feel that a certain trait will work better with your lifestyle (ex: highly active/herding breeds, allergies, better suited for smaller dwellings,etc)?
But most importantly, are you willing to support a system that means that you can have a dog that looks adorable/unique but can hardly breath because it’s been set up that way by humans or has horrible skin can conditions that make it impossible for it to live comfortably?
Are you willing to put in the work to help your new friend be as happy and comfortable as possible?