Of course there are times when it's ok to buy from a breeder. It's a personal decision. Personally, I wanted something very specific in terms of temperament and drive, and I wanted the cards stacked in my favor. All of my rescues have been good dogs that I loved, but had major issues. I wanted to minimize those chances and know what I was getting. I also wanted a dog to compete in IPO with- something that is extremely difficult to find in a shelter (you have a slightly better chance with a rescue), and I'm too novice at the sport to know what to look for in an adult dog that would make them suitable for the sport. I also wanted a dog that would be suitable to work livestock and balanced enough to still be a house pet.
Good, reputable breeders take the time to ensure their dogs go to suitable homes where they won't be dumped, and if life circumstances change they will always take their dogs back. Most of the breeders I know are also active in rescue, through evaluating, fostering, etc. To say that a shelter dog loses their chance when someone purchases from a breeder is ignorant at best. I didn't kill another dog by buying my dog. I wasn't ready for a rescue at the time, so if I didn't buy my dog I would have ended up with NO dog- it's not just "get a dog for the sake of getting a dog, and you have two options."
Rescues are also notoriously difficult. It is EXTREMELY difficult to adopt from GSD-specific rescues around here, especially if you have children or other animals. I've also had bad experiences with shady rescues (and yes, just like there are shady breeders, there are shady rescues). The time will come when I will take in a rescue, but there is only one person I trust at this point (and who I have enough of a relationship with where I'm not just a bulleted checklist on an application).
As for breeding, the really good, reputable breeders do what they do to better the breed we all love. If careful breeding didn't happen, all that would be left are the genetic messes produced by Joe Schmoe with the cute puppies who would still be breeding no matter what. That would mean the end of this breed. Take the time to get to know some GOOD breeders and appreciate the amount of love and time and knowledge that goes into what they do... the work behind studying pedigrees, training and titling their dogs, etc... breeding isn't just slapping a male and female together. My female is pretty much EXACTLY what she was predicted to be when experts looked at her pedigree. It's nice to know what I'm in for... and that I also have the help and support of her breeder should issues ever arise in the future.
Basically, it's not either-or. Many of us here have both breeder dogs and rescues, and many breeders participate in rescue. There's no, "for every puppy produced by a breeder, one dies in a shelter..."