It wasn't socially acceptable to express your hatred, and there are a lot of people who just needed someone to stoke the flames of their biases to the point of hate and violence.
We've watched it become socially acceptable to not keep your biases unchecked and there is a multi-billion dollar media apparatus that pumps 24/7 propaganda into people's minds.
In the past, the stuff we've seen mainstreamed today stayed relatively niche on AM radio and in klan meetings.