Social justice activists speak truth to power by 'cancelling' because often, the speaker is less important 'power' than the person who manufactures and disseminates speakers. Why debate any specific figure on FoxNews - even if you win, Murdoch Corp can mass produce the next Tucker Carlson, just as they produced a dozen such figures before him, and will produce many more after him, canceling their own figures whenever they fail to find a following. It has always been how media operates.

Historically, 'cancellation' often took on literal incendiary dynamics: a 'mob' would burn down a house, lynch a person or group, or otherwise beat someone to death for an unpopular opinion (labor unions, civil rights, and many many others), and quite often, the police would arrest a speaker of such an opinion (teaching evolution, distributing condoms in cities that decided they were obscene, etc). It's fascinating that people believe that 'cancellation' today is some kind of harsh punishment - as if it were anything like how speakers were 'cancelled' 100 years ago.