Lennie's mental disability makes him into a child, with a child's innocence: he likes hanging out with George and petting soft things. Sounds like a great Friday night! Oh, but there's a problem: he's a child trapped in the body of a powerful man. Innocence may protect Lennie, because he never has to deal with the reality of what he's done—but it doesn't protect the people (or pets) around him. Does Of Mice and Men see childlike innocence as the better path? Should we all be like Lennie? Or do we need to be more like George, crushing out our innocence to stay alive?
Innocence is a farce in this book. Even Lennie is guilty of crimes and petty cruelty, and no one is above being awful to others.
In Of Mice and Men, innocence is the only quality that can keep a man from becoming old, lonely, and bitter.