You're right, that guy William Wilberforce--essentially the founder of abolitionism in the West--was really a Muslim. I should have mentioned that. I'm sure Wikipedia will be updated with that information soon.
Seriously, that Wikipedia article is big fat muddle. It essentially lumps everyone who ever said anything against slavery at any point in history in one big "opponents of slavery" list, which really tells us very little. Wilberforce is essentially the father of the end of the transatlantic slave trade, and his driving conviction was nothing but his Christian faith. The transatlantic slave trade was not ended by atheists, secular humanists, Muslims, or anyone but Christians. Truth is truth.
>I’m sure Wikipedia will be updated with that information soon.<
I know well that WP noticeably slants to the Left, often explicitly, but i read some from others who contended that some non-Christian were openly opposing slavery before us. If the Lord leads, sign on to WP as an editor and add what you can verify.