“Going to Africa. Hope I don’t get AIDS. Just kidding. I’m white!”
I'm having a hard time seeing this as 'anti-racism', even if the 'punchline' hinges on the uncomfortable truth that black africans are disproportionately the victims of HIV, it is very much punching down.
Is it in very bad taste? absolutely yes. Is it something that needed to be #1 trending on twitter? no. Is it something that should noticeably alter the path of someone's life? Not in any world I would choose to live in.
I do agree with your premise, a single joke in very bad taste by a non-public entity is a non-event. I think that we all have something somewhere in our closet that could be twisted against us by cancel culture.
The scariest part is that there is no redemption. A picture or recording of you doing something reprehensible when you were 17 will be used against you years later. Cancel culture needs to recognize that people grow and change. We need to recognize that young people say and do stupid shit without understanding the full context of what they are doing, or the potential consequences.