Here's the answer I would have given as an active JW:
When Adam & Eve sinned, they didn't just disobey, they questioned Jehovah's sovereignty, or Jehovah's right to rule. Jehovah allowed the rebels to keep living because he devised a way to restore mankind to imperfection while also demonstrating his right to rule.
By sinning, Adam & Eve passed sin down to their children, like a dent in a cake pan. The cake mix might be perfect, but once baked in the dented pan, it will always be imperfect. Again, Jehovah didn't protect Adam & Eve's children (like Cain or Abel) with HS because he needed to demonstrate to EVERYONE in existence at that time (because there was sOoOo many) that mankind was going to fail terribly and he was the one with the ability to manage humans best. Jehovah needed enough time to pass to demonstrate that all other forms of government would fail.
Honestly, reading your post and my "jw reply" makes me sick. All the excuses for all of the untold suffering is really just plain stupid. I don't know if that answers