"I don't understand how you can say ignorance is a sin and in all the literature I've read, I've never seen it described as such."
That does not mean that my statement is not reasonable.
Your statement is akin to saying to yourself:
"Based upon the people I play tennis with, I conclude that I am the best tennis player in the world."
Obviously your treatment of ignorance is tainted with subjective reasoning based upon the body of literature that you're familiar with or consider authoritative.
Possibly, for the same reason, you are married to the idea of pride being the chief sin.
I'm a fair guy and will give you an example of contexual ignorance as understood by Philo, a Jew writing around 30 AD. It just so happens that he is using the Genesis account as his scapegoat to explain the death of the soul and the advent of evil through ignorance.
Philo (Allegorical Interpretation):
"And the expression "Where art thou?" amidst of being interpreted in many ways. In the first place it may be taken not as an interrogation, but as an affirmation, equivalent to the words "You are somewhere," if you alter the accent on the particle pou "where." For, since you have thought that God was walking in the garden, and was surrounded by it, learn now that in this you were mistaken, and hear from God who knows all things that most true statement that God is not in any one place. For he is not
surrounded by anything, but he does himself surround everything. For that which is created is in place; for it is inevitable that it must be surrounded, and not be the thing which surrounds. (52) In the second placed, that which is said is equivalent to this, Where has thou been, O soul? What evils hast thou chosen instead of what good things? When God invited you to a participation in virtue, have you pursued vice? And when he offered to you for your enjoyment the tree of life, that is to say the tree of
wisdom by which you might live, have you hastened into IGNORANCE and to destruction, preferring misery, the death of the soul to the happiness of eternal life?"
"And if you are content to become the slave of the wise man, you shall receive your share of reproof and of correction, and so you shall discard ignorance and folly which are the destruction of the soul."
"But when the mind, having entered upon the path of wisdom, marches along with its doctrines, and begins to keep pace with them all, it then cultivates the useful trees, which are capable of bearing eatable fruit, instead of caring for those useless kinds; it cultivates a mastery over, instead of the indulgence of the passions, and knowledge instead of ignorance, and good instead of evil.
"ignorance on its own cannot instigate you to do anything"
Tell Philo and Plato that : )