The main thing to remember here is that there are many different ways to provide a safe environment that fits both the needs of the animal and the keeper. For some this may be a Viv for others it a vision cage while still others find it best to use racks.
Over the years of keeping these animals in captivity what we have learned has grown by leaps and bounds every day we find new info and answers to questions. There is nothing wrong with having new ideas and being willing to try different things as long as that doesn't put the health or quality of life of the animal or the keeper at risk.
To say that it is cruel may simply be an overstatement. After all 99.995% of all ball pythons living in a rack have a better life than 100% of all the Balls in the wild. I know that as keepers we want to allow our animals every possible thing our charges could want. But the fact of the matter is that when dealing with the number of animals that most breeders or small hobby breeders deal with we compromise. Wee offer a habitat that meets the animals requirements while giving us the housing space we need.
In the end racks aren't cruel, they may not be the preferred way some keepers wish to maintain their animals. Which is fine but no not cruel.