When Brody is holding a gun on Phoebe and threatening Leo, there is no reason for Piper not to freeze him and disarm him, but she does not. This goes against her entire history and is never explained. See more
You know, you wanted the truth, and I told you. They said you had to come to it on your own. I said you could handle it.
Handle what, that you're what everybody is afraid of, even the Elders?
They're afraid because they don't understand. They can't understand. The Avatars are beyond Good and Evil. They're everything we've been searching for, a life without demons.
...Okay, he's cracked.