It seems the same applies to John Piper if what you stated about his son is true. Should the verses they use to bring down others from the ministry be used to address them? Their response could be, "Do not touch God's anointed."

We have at least two examples from the Scriptures whose children angered God, yet they themselves were not disqualified by God. First, was Aaron whose two eldest sons angered God. Then, there was the prophet Samuel whose sons did not walk according to God's ways.