By induction - repeated exposure to ideas increases their staying power in the mind - see advertising.

If one accepts the premise that fascist ideas spread by exposure, then one way to limit their spread is to limit said exposure.

Sidenote: I'm increasingly frustrated with this increase in veneration of scientific studies, as if studies are the only way or even the best way of attaining or approximating truth. I would like to see more acceptance of lived experience as admissible evidence in matters of debate.