Why are people so cruel?

People are cruel for different reasons. Human traffickers/slave traders are cruel because there is a terrific profit in the slavery of other humans. A quick Google search shows that annual profits from modern day slavery/sex-trafficking/what-have-you amounts to hundreds of billions of dollars. And that's just in one year.

Terrorists often see themselves as liberators and/or freedom fighters. Very often, they are blind to the cruelty and inhumanity of their acts, or justify said acts as part of their overall objective(s).

Hitler rose to power by promising that the mistreatment of Germany by the other nations for WWI would never occur again. In order to do that, he shifted the blame onto an easy scapegoat, the Jewish population. They were already disliked by much of Germany for things done during the first World War. (Things such as causing strikes in munitions factories, which was seen as hampering war effort morale.)

I'm guessing most of the Nazis who took part in the concentration camps became desensitized to the violence that was going on around them. Many of them most likely saw the Jews as subhumans due to all the propaganda labeling them as such. For them, dead and enslaved Jewish people were a normal everyday occurrence.

In a way, I don't think that the people listed above believe that they lost their humanity; they see themselves as saviors, profiteers, and/or just in their causes, and that, in my eyes, is the greatest tragedy.

It's about the language used. There will never be any shortage of brutes to staff concentration camps, but what that infrastructure needs is consent from the populace. To set this up, the language used is carefully chosen to allow the populace to ignore, diminish, or even require the cruelty to happen. So for years language like "vermin", "rats" etc become frequently used, so that the general populace gets used to them. With language, comes concept and expectation.

Bear this in mind when you hear politicians talk about groups of people. In the UK, attempt has been made by politicians to describe certain groups in terms of "swarms".

Honestly, I find the father so annoying. I think he sort of deserves to die on his own merits, completely independent of being a Jew in Fascist Italy.

The way he treats others and conducts himself is considerably deserving of death in and of itself within a Fascist state that would have little tolerance for such behaviour.

In addition to some of the above responses, there are two other thoughts that come to mind for me.

(1) Some people are psychopathic; they do not have the capability to feel empathy or compassion. So, to them, the word "cruel" has no meaning or relevance. They simply can't feel bad for others, even those whom they treat badly. Now, exactly why this is, is something that can fill volumes of psychiatry and psychology books. But, nonetheless, it "is". That is, the condition exists and some people are like this.

(2) Another thought is that some of these Nazi guards were simply "following orders" from their superiors. And, quite frankly, if they didn't want to "be on board" and they didn't want to "get with the program", then they would simply be killed themselves. So, some of them made the mental balancing act of having to decide if they wanted to be the one killed or be the one doing the killing. And, for many reasons, people will choose the latter over the former. Whether or not this is morally acceptable is another story. But, it does explain how and why some people can be so cruel to others.

Here is an analogy. Think of a bunch of kids in a school yard or a bunch of high school kids in their cliques. Sometimes, a group -- likely, a powerful group with some influence -- starts to bully a weak and/or vulnerable kid. There are other kids who otherwise would not want to participate in the bullying. However, they also fear that if they don't join in, they themselves will be bullied. And, for some, it's an easier and better alternative to become one of the bullies than to become one of the bullied.

On top of all these complex psychological issues, there is also the issue of denial, rationalization, and justification. When one finds himself in a very precarious dilemma, it is easy to rationalize his own conduct (even if only for one's own self-preservation).

It's a question of free will.

Human beings are, as far as we know, the most evil thing in the universe.

~ I'm a 21st century man and I don't wanna be here.

I honestly understand and feel for you when you ask that question; however, I wonder if you ask that very same question with regards to what the Zionist Israeli's are doing to the Palestinians. Or is that acceptable?