Once upon a time, when I was in college one of the times (twenty odd years ago), the university debating society invited David Irving, well known Holocaust denier.

The Anti-Facist/Socialist Workers party people got involved, and threatened protests and violence, and pressured the University to not allow the talk.

This started happening then, and not enough of us (including me) spoke up, so it got normalised. Obviously the internet et al has had huge impacts on this (as well as the messed up world we live in), but I do kinda remember those experiences as a turning point, looking back.