Education? If they already know they shouldn't be saying it in public then they already know they shouldn't be saying it in private. Clearly that is an education barrier that needs to be broken down if you, or them, think there is some big difference. Why do you put "impurity" in qoutes? Why do you and others that follow this line of logic always make it sound like stopping hate speech is a bad thing?
So no one should try to stop racism because racists won't change? Lol.So what's the next step if you get them to stop saying any such thing among themselves over the internet in effectively private channels? It's not suddenly going to change their minds when you succeed at that