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. As degiem1 pointed out, Adam and Eve were ignorant of their nakedness and God was pleased with them. It wasn't until Adam and Eve became conscious of their nakedness through pride that they became aware of their nakedness and thus sinful nature.
If ignorance is a sin, it would have been included in the seven deadly sins of pride, envy, anger, sloth, greed, gluttony and lust but it wasn't.
Pride, envy, anger and the other four sins, as well as being nouns, are all transitional verbs. Ignorance is only a noun. Therefore, whilst ignorance can be a factor in the performing of an action, ignorance on its own cannot instigate you to do anything, a fundamental quality if ignorance is to be considered a sin and it's this 'verb' quality that ignorance lacks. Pride, on the other hand can instigate one to perform an action. In other words, pride can make you do something but ignorance cannot because it's not a transitional verb! Ignorance never made anyone do anything but pride has.