I like to think of the times when there was no bible. What knowledge did Adam pass down to his kids? I safely assume it was 'do not sin, God hates it. He removes you from His presence'. Then Cain to his, ''if you sin, run like hell''.The use of scripture can be a divisive thing amongst Christians. Because of all the denominations of churches in Christianity, it is obvious that many people interpret the Bible in different ways. Some of the differences between denominations seem minor, and others seem like outright heresy to others.
Why is this a problem? Well, because the texts of the Bible have been used to support slavery, racism (example –the KKK), and the killing of others. So many people pluck out a single verse of the Bible, or multiple verses, that appear to support their views and their actions without regard for context. Certainly, the Bible doesn't support this, so doesn’t it all boil down to interpretation? Sure, we can say that they are wrong based on consistency in the Scriptures, but what about the interpretations that can't be proven wrong?
Also, what about when the Bible is silent? Firstly, I don't believe that all obtainable knowledge is found in the Bible. If we didn't look outside the Bible, we would be making statements like “insects have four legs” and “bats are birds”. God gave us intelligence and common sense for a reason, so we can use that instead when we cannot find lessons in the Bible about a particular subject. Also, there are convictions that God puts on some hearts that He doesn't put on others. This means that outside the Bible, we do have unique and individual commands from God.
If the Bible says nothing about a subject, does that mean it is opposed? Certainly not! If that were the case then we wouldn't be driving cars, using computers, using phones or doing anything that's been created since the last book of the Bible was written. Yet people continually look for Biblical justification about things, find nothing, and ask odd questions like, “Where does it say in the Bible that we should be doing X?” We cannot and should not be assuming disapproval when the Bible is silent.
All of this isn't to say that the Bible isn't the most important collection of books ever written or that God doesn't speak to us through it. I have had many experiences where something is revealed to me through the Bible almost immediately after praying, but we don't worship the Bible - we worship Christ Jesus. I would trust Him to guide me right even if we didn't have the Bible, because He is perfectly capable of it.
The need to pen the bible (I stand to be corrected) came with the Jews. God chose Abraham. God chose Jacob. God chose Moses. Moses gave the laws to the Jews. The Jews strived to live by the laws. NOT the Chinese. Not the Japanese. Not the Indians. When Jonah went to Nineveh, did he tell them to honor the Sabbath? He told them to do exactly what Adam and Eve would have told their kids...'God hates sin. Do not sin. Stop it, repent'.
So, the Jews were extra 'blessed / cursed' to have 'more' of God's laws. How much more us? Sure the bible does not cover everything, but clearly what it does cover cannot be ignored in the slightest, as God does not lie or waste His time giving ants His commands. Now if we confuse what He has given us with 'clear' precedents like ''God hates sin / evil'' or ''God is good'' .....how mad are we?
The precedents known of God before scripture and those stated in scripture create an acid test that every interpretation of scripture needs to pass. God is good. God hates sin. God is no respecter of persons. God is merciful. Every example you mention, (support slavery, racism (example –the KKK), and the killing of others) fails and therefore there is definitely context missing.