An abuser will abuse regardless of faith or lack of thereof. The proposition that the abuser does it because they are faithless is a fallacy, and a misunderstanding of the structure of morality and ethics.
If a God is your compass, then what freedom do you have? If the god commands to love, you obey. If the god commands to hate, you obey. If the god commands to kill, you obey. For the god is good, superior and knows all. The structure is vertical, and the believer is at the bottom.
On the other hand, humanists takes their ethics and morality values from our common understanding of society. Being empathic, making sure that those who surround us have as much rights as we do. The structure is horizontal, all trying to reinforce each other.