If we reject this premise is there then any possibility to progress into a (hopefully one day) science of ethics? We need to look at such questions from a scientific angle, as the current state of all moral and ethics debate are tied hand and feet to religion. Such questions should be up for scientific debate, this (your questions) are probably not the correct start for the questioning into the realm of ethics but one need to start somewhere.
Anyhow, I would propose an answer of both your questions
What are the most dangerous sentences to say?
Answer: Any sentence containing the words "God wants"
"Which are the most dangerous books to write?"
Answer: Any book containing the words "God wants"
If we start developing our understanding of ethic and moral, and one day is able to leave our current thousand year old dogmatic approach to these issues, I see no problem with having progress down whatever line of science.