Interesting issue.
The only way a breeder could call himself "reputable" is if they are breeding to better the species. For example, if they are breeding
cavies to improve/get rid of genetic health conditions or breeding "show" piggies, as most pet-store rescue piggies wouldn't fit show standards. Guinea pig shows are a huge hobby/ way of life for many people, so there is in this case some need for carefully bred guineas. On the side, breeders could offer homes for rescue
cavies for people who are not looking for a "show-quality" pig.
In this case, I could see someone calling themselves both a breeder and a rescue, as long as they are educating new owners about pet guinea pigs so that the homes are permanent. Otherwise like you all said, breeding will just create a need for more rescue.