It is the concept of "equality" in the eyes of God that changed people's behavior in reality. For if they are equal in the eyes of God, who are we to do less than see them as "equal" too?
No, the concept of "equality" and treating people "equally", is completely a Christian concept that does not exist in a Muslim world view. It doesn't really exist either in an Atheist world view, but they will lie or deceive themselves about that and say that it does, though they can't put forth any scientific or rational explanation as to why atheists should see people as "equal."
Western Culture is based on the Christian World view, and slavery itself was eradicated because it conflicts with this aspect of Christian doctrine.
Liberals have simply taken Christian concepts, such as "equality", "charity", or being their "brother's keeper", and extended them into extremity.
I see your point however slightly disagree. But what you say has merit. Good point!