Quite possibly, this is the cruelest thing that you could do to someone. Particularly when you don't understand it or only know part of the truth (at best), anyway. Let people live; let people learn. (Those are not my words but well said.
Life is about balance. Be kind, but don't let people abuse you. Trust, but don't be deceived. Be content, but never stop improving yourself. The best collection of quotes and sayings for every situation in life.