This seems to me to be a coming of age song, where Mercer begins to lose his innocence as he comes to discover all the lies he was told when he was young (the "rotten tomatoes" that lie in what many people say). Partly, Mercer wishes he never found out about these things ("these weren't meant for us to know"). At the same time, however, he recognizes that this ignorance is what gives bad people the power to do bad things ("we've all got our own knives, sold to the worst of the devils we know"). By believing the lies of what people tell us, we hand over our power to do something good to these "devils". Mercer wishes that he could live an innocent life like he did as a child, but he is torn because he also realizes that this innocence is exploited by bad people.
This seems to me to be a coming of age song, where Mercer begins to lose his innocence as he comes to discover all the lies he was told when he was young (the "rotten tomatoes" that lie in what many people say). Partly, Mercer wishes he never found out about these things ("these weren't meant for us to know"). At the same time, however, he recognizes that this ignorance is what gives bad people the power to do bad things ("we've all got our own knives, sold to the worst of the devils we know"). By believing the lies of what people tell us, we hand over our power to do something good to these "devils". Mercer wishes that he could live an innocent life like he did as a child, but he is torn because he also realizes that this innocence is exploited by bad people.