Cancel culture is the act of removing support for public figures in response to their behavior or opinion. In this way the masses can control how public figures acts or speaks in public (Wiki-article on online shaming).
As an example there has been a debate on J.K. Rowling who has made some remark on gender. This has led to fans banishing her work in order to make her apologize.
Cancel culture has a negative effect on freedom of speech since it is a mechanism used to control how people speak in public. This has led to the publication of A Letter on Justice and Open Debate.