Ferdinand won the Kentucky Derby. He was slaughtered. Had someone intercepted him prior to slaughter, he certainly meets the basic standards for breeding (for the purpose for which he was successful at - yes there are nuances that can be argued but follow me here k?). So a horse may be of quality that falls into bad hands or hard times and then becomes a rescue - does that negate their true quality as a horse that originally made them worthy of being considered breedable? No way - not in my opinion anyway. Does that mean that my spotted saddle horse that I can paint stripes on and wrap in a tarp depsite having the conformation of a gazelle crossed with a water buffalo that is a rescue is worthy of breeding? Absolutely not. However I'm not against breeding to better the breed - whatever the breed - provided that you are breeding for the intended purpose of that breed's goals as set forth in their books.
Here's an example - my well bred TB mare was a "rescue" in that she's off the track and was sent to a dealer, she was hard to handle and had some issues. With time and retraining, she's been amazing coupled with a stellar pedigree and a lovely conformation. I bred her to Mannhattan, an Oldenburg stallion with excellent jumper lines that also has dressage offspring (and some eventers as well). I want a jumper - and bred for such to improve the lines with two horses that compliment each other. Does that mean I shouldn't ALSO be a part of the rescue that is at my barn? Absolutely not in my opinion.
Now take this - *Bekas is a Polish bred Arabian stud, imported from the Royal Polish Stud know as the Janowski Stud, and bears the royal brand of the crown over the J, and his stud number. His lines were those that were rescued in WWII by Macarthur and were used to found the Polish Trakehner breed, as well as influence several other European WB breeding stock. Now get this - HE IS A RESCUE. He is now 29 years old - and likely no longer viable. But if he was, could you imagine NOT breeding a horse of that caliber and history? With movement, a show and race record, and breed recognition that spans not just studbooks, but decades???
See my point?
Breeding has its place when done right. If everyone wanted to do the same thing there would be no need for different breeds. If someone wants to go to the Olympics, or the highest levels of whatever sport they are at, does that mean they HAVE to have the best bred of the horse of choice? No, but it sure helps. Now THAT said...these days, there are things that are rescues showing up at auctions and rescues all over the country that would knock your socks off....just look at Bekas. But yes, those finds are few and far between and take a very VERY good eye!