Yes, sin didn't exist on earth yet. That is why it was good to him. Nothing bad had happened yet on earth. At that moment, the tree of life was good. Nothing bad resulted from it's presence or it's power.
Example:
If I grow marijuana, it's just a plant growing in my backyard.
I I grow marijuana, harvest it and sell it to someone, and they get stoned with it, it is sin
This person could not sin without my effort to assist him in this sin. So he is responsible for his choices, yet I am also responsible as he couldn't have gotten high and committed this sin without my assistance.
The evil is in my yard (hypothetical) what is derived from the evil I chose to grow in my yard is sin yet I chose to grow it and let sin loose into the world, via the drug marijuana.
That's my point. We are responsible for what we do in a sense, yet we also need to be fair and weigh the conditions which caused the sin. The conditions and circumstances surrounding the sin are weighed to determine responsibility.
Here is an example of a story from another thread. Man shoots wife's lover, yet
she is sent to prison for it. He committed the grevious sin, yet the conditions which steered him into this sin were weighed out thus he is not totally responsible. Without his wife crying rape, the sin wouldn't have been committed, we assume.
http://www.baptistboard.com/showthread.php?t=49511