This is interesting. To a person hearing this for the first time, it seems that God is content that some ants wander off. He might wish for all the ants to cross, but it doesn't appear that He is willing to do anything about it. I didn't think you thought that God stays out of our lives. I know you know all the verses about Christ leading His sheep. Does God offer a path and then stay out of it? God Himself gave the ants the ability to be curious, so when they exercise it, is that too bad for them?
Me: "was it God's original plan that all people would be born immortal on earth, but man foiled this plan?"
Maybe you should ask yourself if God made Adam and Eve in Paradise so they can become corrupt and die? Did God destroy His own crown-jewels intentionally? ... I think it makes more sense that we are the culprits of the destruction of our own blessings rather than God, Who, after, all gave them to us.
God created Adam and Eve fully knowing they would become corrupt and die, He gave them that ability (can become), so the answer to your first question is 'Yes'. (Is that bad? :)
I don't think God destroyed anything in this sense, as He is not the author of evil. God could have created us as perfection, but He didn't. He included the potential to sin. This was done for His perfect purpose, but it is nonetheless true. I would agree that we are to blame for our own sins.
I believe God's plan incorporates His perfect knowledge of our sins, AND His unwillingness, at times, to interfere with their commission. Of course, other times God prevents us from sinning through the Spirit.
God does not impose. He only offers.
God created Adam and Eve fully knowing they would become corrupt and die
God created Adam and Eve with the full knowledge of what effects their free choice will have, not what choices they must make.
The resulting sin and death were simply the effects of ancestral parents' free choice which included not only their decision to disobey God, but also do refuse to repent.