What a sloppy, ignorant brush with which to paint such a complex subject as abolition. Religion was, and is, used to justify slavery every bit as much as abolition. In the U.S. for example, every major southern church organization was founded explicitly for the purpose of supporting slavery; the Southern Baptist Convention didn't officially renounce this support until 1995.

To this day, religion continues to be a powerful driver of racism, classism, and slavery. In case you need examples, may I point you to the Hindu caste system and the Muslim doctrine of Dhimmitude.