Benefit of failed human cloning

Many diseases can be traced back to the genetic material being turned on and off in the egg after fertilization. When we first started cloning we didnt allow the DNA to to go through this process and thus dolly the first successful cloned animal, died from numerous genetic diseases. If we were to do the same with human DNA and clone one incorrectly, we can trace many genes that make a person autistic, have varying cancers and other problems. Then through isolating many genes for certain disease we can make gene therapies that can halt, stop or even cure. Considering that isolating the genes by sampling the genome of certain groups of people with said genetic problems it would take a much longer and more expensive process. Other then ethical problems which many will bring up, due to the unavoidable death of the clone, is the thereotically sound?