You're misunderstanding what the idea is. The idea is to show german children:
That person has that opinion and they may think it, but the opinion is wrong. We had a huge big argument over it, some people call it WW2, and the result was: Their opinion is wrong. So we decided to let that be the last argument about it and not let them start another argument, because the question has been answered at length.
I was referencing one of the original comments made by a German far-right politician on Facebook that started the debate about the responsibility of platforms like Facebook in moderating hate speech which in turn resulted in the law the article describes:
https://translate.google.com/translate?sl=auto&tl=en&js=y&pr...
It's not a slippery slope in this case. I admit it's a bit unfair to reduce psyc's argument to this but the language the law covers is entirely in the category of "people openly demanding that certain other people be killed or subjected to violence". Facebook dragged their feet to moderate comments like these and the law is a response to create a legal tool to force companies like Facebook to moderate hate speech or face serious fines.