I agree with Bruce when he says that many people adopt a snake and call it a rescue.
My definition of a "rescue" is a snake that when I take in is in bad shape.... either several layers of stuck shed, sick, underweight, parasites, etc. . Sometimes I will give a person a couple bucks for them, but even if I do, if the snake is in bad shape when I get it, it is considered a rescue.
When I get a snake for free or cheap, and there is nothing particularly wrong with it, I consider it an adoption. If someone wanted me to adopt a snake, but told me that it could never be bred, I would refuse to take it. No way I am going to care for a snake for 30 years and not do with it as I please.
I have / will turn several of my rescues into breeders. As long is there isn't something fundamentally wrong with the snake after rehabilitation, why wouldn't you? Once you take over the responsibility / costs of a rescue, if you choose to breed it is your decision and nobody elses business... including the person you got the snake from.
"Rescues" once they are healthy again IMHO can make some of the best breeders. I have several females in my collection that were 5+ years old virgins when I got them. That is a BIG, fully mature momma that is just waiting for her opportunity to lay a BIG clutch!