Interested one,
I didn't make the claim rather God does. Since I couldn't disprove that sin causes death and in my opinion science gives support to it being a possible I put faith that the creator would get that right. Trust me like yourself I do question everything and I'm not afraid to explore all views. For me the cause of death being sin is a logical explanation that can harmonize with science quite nicely, albeit it requires an element of faith. Unfortunately it's something I can't say that God said in so and so scripture that the method of choice was to cause DNA to deteriorate causing death as a result of sin, no more then I could say science proves sin doesn't cause death. The element of faith is still required either direction one decides to take.
I respect your view and thank you again for your question as well as your valuable contribution to the topic. It was an intelligent query and I hope that I was clear enough in my attempt to answer.