Use the following excerpt taken from an abolition speech delivered by william wilberforce to answer the question below:

"…i must speak of the transit of the slaves in the west indies. this i confess, in my own opinion, is the most wretched part of the whole subject. so much misery condensed in so little room, is more than the human imagination had ever before conceived let anyone imagine to himself 6 or 700 of these wretches chained two and two, surrounded with every object that is nauseous and disgusting, diseased, and struggling under every kind of wretchedness! how can we bear to think of such a scene as this? "
--william wilberforce's, 1789 abolition speech

based on the above excerpt, why did wilberforce think that slavery should be abolished?