Not necessarily? More like by default. Purebreds are a thing because of certain genetic traits and are bred to not only maintain them, but to enhance those traits. Because of all that inbreeding the propensity for certain diseases and cancers are vastly increased. A purebred dog or cat will with near certainty be riddled with cancer or disease by the time they start getting a bit older. I love both cats and dogs, but purebreds shouldn't be a thing.