By my estimation -- and there are certain individuals where this might not be true -- if you support this you likely _want_ this to be a continued effort to remove objectionable content.
I find most religious content to be objectionable. But for the most part, it is benign. In general, someone's religious beliefs don't affect me. Once it starts to call for the ill treatment of others, though, I think it should be removed. So religion-based anti-LGBTQ content should be removed (for example).
Holocaust denial stems from a long history of anti semitism, which in itself tends to advocate the poor treatment of others and enbraces a certain amount of dehumanizing language. All for something they cannot help and doesn't actually affect others. We know that hate groups embrace this. We also know it happened - we have pictures. It is simply lies to get folks to treat others badly. So, removal.
Should Newton stop being explained beacause he is flawed? Or do we need a disclaimer in every single video about mechanics?
What about photons as small pieces of matter?
Ehat about the existence of God?
Edit: oh, I see. You're one of several responders who have latched onto OC's use of the word "reasonable" and are disengenuously attacking that word outside of the actual context. Excellent example of attacking the weakest form of somebody's argument and applying the slippery-slope fallacy from there. We can do better than this, folks.
If you want something more generic, you could start with hate speech laws in Australia, Belgium, Canada...Spain, Switzerland, the UK, etc. Or even more generally, the UN's International Convention on the Elimination of All Forms of Racial Discrimination.
So, there's plenty of established frameworks to base your work off of and they've been around long enough that we can measure what the impact is.
As a matter of fact, the answer is: Facebook. That _does_ seem like the issue to me.
I think that you're moving the goalpost from "who decides" to "is it a good idea". To which I've already answered: yes, it has a proven track record.
If you ban Holocaust deniers, then you're in the business of drawing lines, proclaiming what is truth. This is a powerful position and many will wish to use it for more than just the Holocaust. They will initially do so by presenting a variety of outrageous content which maybe should be banned, applying public pressure, and their initial targets will be reasonable.
But the outrage industry is big these days, and its targets are many. I shall present some recent evidence of its working. Consider a figure like, say, Bruce Gilley, who I was just reading about this past week: he's an academic who says non-mean things about colonialism. A public outrage drive, started by Maoist philosopher Joshua Moufawad-Paul (author of "The Communist Necessity") got his publisher to cancel a biography of Sir Alan Burns; similar outrage drives have previously attempted to see his doctorate revoked. I have not read his scholarship and have no reason to suppose his work to be excellent; however, I should prefer that academic degrees are not revoked after the fact for failing to conform to any particular orthodoxy.
Yet these are the times that we live in: we are increasingly censored by the mob. Facebook content moderation is an obvious target and there is no doubt will be targeted. The categories will expand. Facebook's resistance to such measures will either be heroic, or profoundly inadequate.
So consider: Is the Republican party under Donald Trump a hate group? Is it legitimate for them to have Facebook operations? Surely if you work in Silicon Valley you know someone who considers it a hate group, and believes it should not be permitted a Facebook presence. That is where this ends up. It is not a long and tortuous path. And as hateful as Holocaust denial is, it is possible that Facebook might make the world a better place in the end by allowing it, that they may say, "We are not the content police. No one is."
Taking steps against that are thus justified.
Take, for instance, this overtly right-wing partisan here, John Stossel, also writing within the past week: https://pjmedia.com/columns/john-stossel/2020/10/07/fake-fac...
I have little traffick with John Stossel's work, and will not attest to any specific claims about wildfires, but Facebook's idea of "fact checking" this specific video involves groups like Climate Feedback, who are apparently empowered to lie about Professor Stefan Doerr of Swansea University reviewing his video.
This is not about Stossel, whose work I will not condone here. This how much you should trust Facebook to be an effective arbiter of Factual Truth, which should be very near zero. And there's a word for enforcing the "Factual Truth" like this: it's called Orthodoxy.
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Might as well vehemently argue that the earth is flat, if you think the Holocaust was faked.