I would suggest any holocaust deniers who are still ignorant and purposely so (like the Iranians) cannot have their minds changed, and therefore can justify anything - which makes them inherently dangerous. They certainly cannot be trusted with nuclear technology. However, HBO films has put together a very compelling documentary about a film made by the BBC and US during the end of the war. Camera men from the BBC, US and even Russia were sent out with the troops to film what was going on in the field and the horror that is shown is simply devastating. The film was never actually shown for the past 70 years, until now.
It's called Night Will Fall. It can be found on Youtube at the following link: Night will fall.
The problem is, these scenes are now being repeated, by ISIS, in the Middle East.