Nobody claims that atheism brings inner peace, although abandoning the tyranny and terrorism of hell theology goes a long way toward restoring equanimity in those tormented by it.If atheism brought inner peace, everyone would embrace it (except those who enjoy being conflicted.) Instead, the majority of people embrace religion.
"To the philosophy of atheism belongs the credit of robbing death of its horror and its terror. It brought about the abolition of Hell." - Joseph Lewis