The Talmud makes it clear that death came into the world because of Eve. Had she not eaten from the Tree of Knowledge, and convinced Adam to also partake, people would have lived forever.
We are also told that the same state of innocence and purity, returned to the Jewish people, at Mount Sinai. They were on such a high level, that death would have been eradicated, had they not sinned with the Golden Calf.
The Keli Yakar does not put all of the blame on Eve. It was Adam that gave the message to his wife, that it was not only forbidden to eat from those special trees, but it was also forbidden to touch the tree. He thought that adding the prohibition of touching the tree, would give his wife added protection from sin.
Eve did not realize that this additional precaution of not touching the tree, came from Adam. She thought it was from Hashem Himself.
The Serpent epitomized evil and cunning, and used this misunderstanding to his advantage. He pushed Eve to touch the tree, and convinced her that just as nothing happened from touching the tree, only good would come from eating it.
It is so important that we study Jewish Law thoroughly, so that we are able to know the difference between Torah law, Rabbinic law, custom or חומרא, stringency.
If we do not possess that level of scholarship, we should be certain to ask the person that tells us that something is forbidden, to explain why. He should be to tell us the specifics of a particular law, and its origin. If he cannot, he has no business telling us of this prohibition.
We learned this lesson from Adam and Eve. We paid a heavy price for this lack of clarity. Such situations must not happen again.