Was Rhodes a racist bastard? Undoubtably, but he also paid for the construction of Oriel college and the creation of the Rhodes scholarship which was run by the Rhodes trust (now the Mandela Rhodes Foundation), in fact Mandela said that this was a chance to close the circle of history.
I'm not defending Rhodes in any way shape or form but there is more to his story than his actions in Africa and it would be difficult for a college to get rid of the statue of the man who paid for it's construction.