Marrus is a fine fellow, a respected scholar and a distinguished citizen.  But put yourself in the black junior fellow's shoes. A powerful privileged Canadian has just belittled you and called you a slave. Funny? Or have you just been squished, put in your place? Shamed?  This is how we need to look at power imbalance and racist humour. Not to defend the perpetrator but to advocate for the human being on the painful receiving end of the "joke".