Why sometimes Humans are worse than animal?

I just have had my class of conflict resolution yesterday... the docent gave decent example of brutal conflict happened in the world. He mentioned about the state rape done by Serbians toward Bosnians, or Nazi toward Jewish, Indonesians toward their local chinese.

Questions pouring in my mind... even animal wont do such things. Why humans sometimes are worse than animals? I remember my docent quoted a serbian soldier answer when he was put in trial for raping women: he did it so that the Bosnians would bring their seed and thus, there would be no pure bosnians anymore. wtf? I simply couldnt believe it.

How come these ppl who call themselves humans comitted such things heartlessly?

Jam it back in, in the dark.

Many people did such cruel thing to other only because stupid reason: "You are different than us, so that you should die". What Do you think about ethnicity? Is it a big problem or huge problem to be taken care of? Is that so important that people must kill each others because they are just not same?

I couldnt understand what those people had in their mind, really.

There's nowhere I can't reach.