Why were the writers of the Bible so obssessed with cruelty and sadism - maybe they were mentally deranged?

There are some unavoidably difficult passages in Scripture, but the Hebrew God was incredibly progressive compared to the surrounding cultures. The Hebrew God may have commanded "an eye for an eye," but the norm for that time period was "your entire family for an eye." You need to look at it in context. The Bible is also extremely progressive, even by today's standards, concerning treatment of the poor and marginalized. The Hebrew God commanded that every 50 years all debts be forgiven and land be returned to its original owners. It was called "Jubilee."