He didn't really deserve what happened to him

He actually never denied the Holocaust.

I am not a Holocaust denier, an anti-semite, or even a Holocaust revisionist, but I don't think there's anything morally wrong with honest attempts to revise history. In fact, historical revision is, in every other context, widely recognized as a legitimate pursuit of historians.

--
"If there's nothing wrong with me, maybe there's something wrong with the universe."

"He did research from an entirely un-partisan point of view."

Well that's what he said in the film, but I am skeptical. God knows what his original intent was, but after he testified about his results in Zundel's trial, he voluntarily became a spokesperson for Holocaust denial, travelling around to conferences etc. Possibly he was motivated more by the desire for attention than anything else.

"it was later explained that any cyanide used in the mass executions at Auchwicz would have washed off the walls over the passage of time."

Not exactly. In the film it was explained by the lab technician who performed the tests on Leuchter's samples that any cyanide residue on the surface of the walls would have been diluted beyond recognition in the lab because Leuchter dug too deep into the walls. Furthermore I believe it was explained by a historian in the film that the gas chamber Leuchter tested was a reconstruction done by the Polish government, and that the bricks from the real gas chambers might have been used to build apartment buildings in the vicinity.

Joshua Hirsch

The Forensic Institute of Cracow completely rebuked Leuchter's findings. They used more advanced techniques and did find traces of cyanide. Leuchter admitted at Zundel's trial that he had no degree in science or engineering. I do not feel sorry for the guy, really, he let himself be swindled by Zundel, and ruined his own legitimacy and reputation. I do not think he was ever sincere about his findings; he was simply chosen because was an expert on methods of executions, and Zundel needed some kind of intellectual or pseudo-intellectual to speak in his defense.

I'm not so sure that his research was un-partisan.

The only place you hear the voice of Errol Morris is when he asks the final question:

"Have you ever thought that you might be wrong or do you think that you could make a mistake?"

and I think Leuchter makes a bit of a Freudian slip with his answer:

"No I'm past that. When I attempted to turn those facilities into gas execution facilities and was unable to, I made a decision at that point that I wasn't wrong..."

Sounds like he's telling us he already believed that the gas chambers were not actually gas chambers and that his 'research' just helped him to cement that belief.