Well that's what most people think when it comes to innocence.
Usually the logic goes like this - If I don't know about 'x' (ignorance) therefore I am innocent of 'x'. Lots of terminology in the news, religion and other philosophies work on this kind of thinking. It's basically the foundation of a lot of things. You may not think of it that way.
Think of this common term - 'Think of the children' when a horrific event happens. We want to shield the 'innocent' from the event. We want to keep them ignorant and avoid having to answer questions usually.
I'm sure you know of other terminology possibly from your own culture that matches that.
A famous religious saying is - 'Ignorance is bliss'