There are reputable breeders who do not insist upon neutering and spaying. Those that do are usually only concerned that their line not be diluted or they want to limit the competition in breeding. It is not usually for the well being of the animal.   
I personally don't know any responsible breeder who believes this.   
Intact females need to be watched closely for Pyometra and mammary cancer.    
Intact females are bombarded every heat cycle with the same hormones pregnant bitches are.  Not breeding them increases their risk of uterine infection and mammary cancer.     |