Say for instance I have a dog who I consider the best cur dog that ever hunted. Now you also have a buddy (we all know one) who has a piss-poor dog that he seems intent on always hauling around. One day that piss-poor dog ups and finds a hog ahead of everything thing else. Do you start culling curs?
One of my absolute best dogs a couple months ago took a notion that when I turned him out of the box he was going to straight shoot me the finger and crawl under the buggy. I usually don't do this, but this went on for a few weeks until one day I had enough and he got the raw end of a pretty good switch. Didn't take long and he got his mind right. According to what I'm reading, I suppose now he's a cull.
I don't think either of those comparisons really apply in this situation.
I do however agree that dogs are not machines.
And like scott said , if the dog is half cur I would not hold him to the same standard and would not consider him a catchdog.