The Atheist Obsession with Insulting Christians

[ApeNotKillApe]

"I already mentioned Dietrich Bonhoeffer but you can add William Wilberforce[...]"

"the question is whether they were motivated by their unbelief to do so in the same way that the Christian exemplars were? In other words can you honestly say that any particular social reformer or hero stood up and said that their atheism compelled them to fight for their cause? Please give me an example."

William Wilberforce was a devout evangelical Christian, true, and his conversion was clearly a catalyst for his dedication to self-criticism and introspection, the practice of moral reasoning, which naturally led him to his convictions and his contribution towards the abolition. 
Wilberforce's intent was motivated by his religious conviction, certainly, but the intent does not justify the deed, nor the deed the intention. 
Abolition of slavery does not, in any way, shape or form embody the principles of Christian doctrine.

Throughout the entirety of the New Testament, Christ does not once express any objection to the ownership of a people.
The apologists haven't even found a vague quote to reinterpret as a condemnation of slavery.
The most attention he ever pays to the subject is in the form of this little parable: 

Luke 12:45-48: "The lord [owner] of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers. And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes. But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more."

 
The Messiah himself used slavery as an analogy for the Christian worldview.

The Biblical scriptures contain instructions on proper treatment of slaves, the instructions do not in any way condemn abuse or mistreatment of human beings, they are administrative procedures concerning management of chattel.

Considering his views as the Bible portrays them, I think it's fair to assume that the Atlantic slave trade was either of no concern to Yahweh, or the passing of the 13th amendment left him feeling disappointed. 
William Wilberforce may have been condemned to Hell for challenging slavery; and in the event that he wasn't, Wilberforce ascended into Eternal Paradise and in stood in the presence of God to discover his Lord and Savior thought his pursuit of justice was boring and kind of dumb.