Of course, one legitimate question would be whether someone like Himmler was simply a madman and a fanatic, which is also the same thing many people have asked about Hitler over the years.
Certainly they were evil men who followed an extremely racist ideology in which the so-called 'Aryans' were the Master Race and everyone else was there to be plundered, enslaved and exterminated. That's what Nazism really was at its core, along with the idea that they all had to obey all of Hitler's orders to the letter--and often did their best to exceed them while feathering their own nests along the way. Ultimately, the war they started also left their own country in ruins as well.
Were they just crazy? I don't think they would have gotten nearly as far as they did if they could just be easily brushed off like that. From Hitler on down, a number of them showed symptoms of a wide variety of mental illnesses, but they also seemed highly functional in taking power, setting up a dictatorship and very carefully preparing wars of aggression, so their madness did not prevent them from doing all that. Most of them just came right out of nowhere, but they were organized and cunning enough to take over Germany when the opportunity came.
They had some very weird and unconventional ideas about science, too, and ended up building all kinds of weapons that were ahead of their time. Even so, looking at the ideology of someone like Himmler, I'd have to say that it included a mishmash of kooky ideas that he picked up from his own reading.
There was a very famous incident on the Eastern Front in 1941, with Himmler observing the mass shootings carried out by the SS Einstazgruppen near Minsk. He decided that this type of extermination was too hard on their own men, which is why he ordered them to start experimenting with gas chambers instead. Supposedly, he almost threw up when he saw the dead bodies in the mass graves.
"In August 1941 he had an experience that may have speeded up the extermination program. On that day, SS officer Erich von dem Bach Zewelski stood beside Himmler as he watched an Einsatzgruppe (SS extermination squad) shoot a hundred people, including women, in Minsk. He reports:
"When the first shots were heard and the victims collapsed, Himmler began to feel ill. He reeled, almost fell to the ground, then pulled himself together. Then he hurled abuse at the firing squad because of their poor marksmanship. Some of the women were still alive, for the bullets had simply wounded them." [Graber]
A residue of humanity, then, that made him ill, led Himmler to order soon afterwards that women and children should be killed in gas vans - a decision that led to the gas chambers of Auschwitz-Birkenau, the largest of which could hold up to three thousand victims at a time, and where Eichmann reckoned that two and a half million Jews alone were systematically murdered. [Hoess]"
Gen. Bach-Zilewski was one of the biggest mass murderers of the war and shot hundreds of thousands of people in Russia, but he was also concerned that it was turning his men into psychopaths who were "finished for life". They began to build gas chambers because they thought it wouldn't be as hard on their own men.
The Nazi newsreels showed Himmler visiting the ghetto and concentration camp at Minsk, but not his attendance at the mass executions.