
This is a moot point. Most of the people who supported slavery or owned slaves also called themselves Christians, as well as most of the abolitionists and most of the slaves. It was the predominant religion at the time. Certain denominations leaned one way or the other but I don't the whole religion significantly leaned either way. The North/South divide was the main factor.
Abolitionists were using Exodus to say slavery was wrong, for what should be obvious reasons to anyone who knows the general plot of Exodus. Slavers were using the latter, lesser-told, parts of Exodus, the parts where the Hebrews immediately got their own slaves as soon as they got their own country, as justification for slavery.