I would argue that MLK didn't practice anything like what we see in today's cancel culture, which I would characterize more than anything by it's lack of (and fear of) sound logic and discourse. People nowadays are labelled as bigots just for asking questions - which doesn't make any sense! It's fundamentally an idea that people never learn, grow, or change their minds, and that anyone is evil if they've ever questioned any of our tribal myths at any point in time. MLK, to my knowledge, didn't ever have any similar messages, and is therefore not at all an example of how cancel culture is a positive strategy.

On the other hand, MLK's murder is a prime example - you could say the pinnacle example - of cancel culture. MLK argued his points with poise and logic, and was killed for it, because some people couldn't handle the truth, and had no valid responses other than to cancel him completely.