Why are there so much cruelties against fellowmen in the Holy Bible?

Because The Bible is a 100% truthful record of how people are. People are cruel. People are vindictive. People tell lies. People pretend to be someone they are not. People do things which they condemn others for. People deny the truth of the world that is and of the truth about themselves. People are proud. People hide behind all kinds of masks. People go on self-righteous crusades when they themselves are full of hate. The list could go on indefinitely. Just read the newspaper. Man has not changed. Man still needs God so desperately and still refuses Him. If the world in turning away from God, as did those people in the Bible, is getting better as a result, then the evidence is lacking.