Is English your first language? I ask because you seem to have misunderstood. What you have quoted is a linguistic device which suggests that because some black people are not offended does not mean that all black people are not offended. It also suggests that some white people assume offence on behalf of others and I doubt you can disagree with the truth of that.

Where you infer a "blanket and unqualified characterisation" is in your mind not in my comment. I accept absolutely that many people will not be offended by Blackface Border, I am not offended, but many might well be and it is something that such Border teams would be well advised to consider.

More generally, I am not big on this causing offence thing. People take offence as they will. Somethings offend me that are not even against any law and even if they were, I would not pursue it.