Five years for slander?
How many people in the US would be in jail by now?
It's been noted that a lie, repeated often enough, becomes accepted as truth. There are people who would like to rewrite Germany's history and denying the Holocaust would be beneficial to them.
As we have learned from history, if indeed we have, ideas have consequences. A future generation of Germans, having learned a different version of Nazi history than the one we are familiar with, might make the same mistakes their predecessors made, with similar consequences.