First of all, denying various genocides is already a felony in many countries. Holocaust denial is antisemitism, antisemitism is a hate crime. Generally we tend to oppose genocides and whoever caused them. Denying a genocide is halfway approval of said genocide. It is a mark of historical revision in favour of the antisemitic side.
'Those who were persistent in hypocritical conduct and disputatious in hypocritical speeches; who studied what was wrong, and went on to do so more and more, and whoever increasingly followed what was wrong so as to bewilder the multitudes: these were put to death. ... These four classes were taken off, and no defence listened to.' (Book of Rites 5.50) Nowadays, we probably don't have to put people to death, but such people should definitely be prosecuted to prevent the further spreading of lies.
I understand the importance of the horrors of the holocaust and I believe it happened; but what kind of nation would we be if we started imprisoning people for their beliefs? What happens when a government actually does stage a false flag and people are arrested just for questioning it? This should not happen.
At the end of the day it simply does to matter if you are a conspiracy theorist or just an idiot, the Holocaust was definitely real. I still struggle to understand what one gains from denying such a horrifying genocide, but if that's ones cup of tea then by all mean, be looked down upon by society.
To say they deny that the holocaust happened means they are rejecting facts. We don't consider it a felony to deny that the Native American Genocide happened. Plus, they know what it's true, they just deny it. There might be a deeper reason as to why one denies something widely accepted.
I may hate the people that deny the holocaust and I might disagree with all of their beliefs. However, I will do whatever I can to ensure that they have the right to those beliefs without prosecution. We laugh at other countries and call them ignorant when they punish people for having different religious beliefs or different political beliefs- but we are here asking this question?
Holocaust denial is stupid. The evidence shows it happened. However, if they can outlaw belief in falsehoods they can easily outlaw belief in the truth as well. Let people have and express their own opinions. Truth always wins because truth has real evidence behind it. If we rely on state power to suppress expressions of things like holocaust denial then eventually the state will lie and call something true false and prohibit the expression of it.