Why are Holy books tainted with ancient tribal hate and cruelty?

The Holy books (I ume you are talking about the Bible) reveal the true history of the nation of Israel. The tribal hatred is recorded because it existed. The Jews were loathed, despised, and hated because everyone knew that their God was real. The only reason that their enemies were allowed to conquer them on several occasions was because they continually turned their back on God as a nation, which is the point of the lesson.