First of all, we know that deplatforming racists/fascists does actually help to stop the spread of racist/fascist ideas.
How do we know that? Has a study been done? Are there surveys that track it over time?
Racists beliefs have decreased over the past 50 years. I haven't seen any evidence it's spiked since the advent of the internet.
More visible? Sure. But more visible doesn't mean more people hold those beliefs.