Interesting that you use a rottie as an example......
I know we are lucky--we got Jada at the SPCA, and she is just about the sweetest thing on 4 legs. When we got her, our neighbors were not happy, but we brought her out to meet the kids, and all she could do was lick all of them. I know this is not always the case though, and we are fortunate to have such a sweet girl.
I like Amy's point about getting the experience of raising the dog from a puppy first (in her case, a husky). We had beagles all my life growing up, so I knew what to expect with Abbey. Riley was just a tiny pup when we got him, and he doesn't have a mean bone in his body. As for Jada, my husband raised 2 rotties before--and they are sweethearts too! I hadn't had the experience with a big dog like her in the past, but he has, and he just knew she was a great dog--and he was right!!!
Kito was 8 months when we got him. Shibas are a handful--I wish we had gotten him as a younger pup, so he could have been socialized better, BUT I wouldnt' trade him for the world.
As far as what the original post was about, maybe the person has good intentions, but cannot find what he or she wants at your local shelter. Maybe they knew that was what you wanted to hear. Everyone can't be convinced to adopt and rescue dogs.
I work with a guy who wanted a golden retriever pup. I gave him the number of the Golden rescue here, and at the time I know they had a litter of pups. Guess what? He drove an hour away and got a pup from a breeder. That doesn't make his dog any less of a beautiful wonderful pup, and it was his decision.
This argument could go on and on (and I have a feeling it might). The bottom line is, no matter how much we all advocate rescuing, unfortunately we can't control everyone to do the same.