Huh? Sounds like he was trusted, but they verified his work. Trust != blindly accepting someone's work. And in the end, this intern violated the trust that _had_ been placed in him, and he was shown the door. Rightfully so.
Yes, part of growing up is making mistakes. But, part of growing up is also living with the consequences of your mistakes. And, yes, I've made some mistakes in my youth (hell, even as an adult) that have led to professional consequences, including termination.
Further, it's up to every manager and employer if they want to continue this kind of fear and punishment, or accept and correct mistakes. I don't think the entire professional world acts like this in reality, only in dystopian entertainment and nightmares.