It reminds me of the law in Germany according to which Holocaust denial is a crime. And a slippery slope it is; before you know what has happened, you become precisely the thing you fought against so hard.
Afriforum will never again have the kind of political power that would render their opinions potentially dangerous. So what if Kallie think apartheid wasn't a crime, or even if he thinks it was a good thing, or even if he thinks black folks are all a bunch of retards? It's a bit like watching a little pit yorkie yap at a rottweiler. Who the freck cares what he thinks - he doesn't have any power to enforce any of his ideas.
I am more worried about entities that do have such power instituting laws that will violently impose ideas on other people.