Of course people of faith aren't mentally ill. As someone who has a mental illness I can assure you it is nothing like having a belief in God. Dawkins thinks he makes some profound statement when he says something like "who created the creator". Any freshman philosophy student can answer that question with ease. Also the definition of faith is sort of a popular one and is not really the accurate definition. As the great philosopher Dr. Craig says faith is "a way of trusting in something that you think or know to be true".