I don't understand, if he wrote an op-ed uncovering racial discrimination in academia, why would people who are (presumably) against racial discrimination want to cancel his lecture?
> why would people who are (presumably) against racial discrimination want to cancel his lecture?
Because they are not against racial discrimination.
In 1984, there is a scene at the end where O'Brien (a party member) interrogates and tortures Winston (the main character). He asks him political questions and demands truthful answers, and if he spots that Winston lies to avoid pain, but knows the truth, O'Brien still electrocutes him. At the end O'Brien shows him 4 fingers and asks how many fingers Winston sees. He says 4! And gets electrocuted. Then he says 5, and gets electrocuted again. After many attempts, Winstom cries "wtf it matters how many fingers are there! it's whatever number you want!" O'Brien, pleased finally, releases Winston. O'Brien wanted to teach that truth shall not be appealed to in presence of authority, for the only truth is the will of the authority, and when the will changes on a whim, the truth does too.
That would be because they are in fact racists.
Because they redefined the meaning of word "racism" such that their views are no longer considered racist. Unsurprisingly, that also redefined the meaning of "against racial discrimination". Tl,dr: We no longer understand each other.