I do not agree with you. The books Shmiras HaLashon and the Chofetz Chayim detail how life and death are in the power of restraining one’s speech. Those books are both available with an English translation. Anybody who does not live near a Jewish bookstore and wants to read these books can order them online; and he should, because they can change his life for the better! The Chofetz Chaim, in English is incredibly good, but both books have the power to get him where he needs to be spiritually.
The books you are talking about were written by men, wise men, but men nevertheless. Leviticus was written by inspiration of God.