The Bible says men should not eat certain foods (pork for example). Yet men have learned over the years to properly treat such foods to prevent disease, to prepare and eat it safely.
Remember, Hell was previously Hadees, and before that Sheol. Over the years, and the bible was translated from language to language to language, and words and meanings were not always accurate. It went from a state of "absence of God" to a physical place of fire and torture.
My point is, we have learned over the years men have found that the Bible is not 100% correct. It can be wrong. And if it can be wrong about slavery, about eating certain foods, about where and how plants shall be grown on farms, etc then it can also be wrong about hell (which may be in the afterlife and only 1 man has returned from death and he didn't stop in that particular place). I have no quarrel with boundaries that have been set for us to live our lives, but I do have doubts about a place of hellfire for men who live good lives but don't believe every word in the Bible.
You say that only one person has ever returned from the dead. On what basis do you make that claim? The bible? Remember, you claim that it is full of errors. If someone made up hell, they could also have made up heaven. Or the resurrection. Or salvation. Or Jesus. It could all be a sham.
You can't pick and choose the scripture you will believe on the basis of what you think is "right" or "wrong".
Thank you for giving a reasoned post. If I may butt in, the Church teaches this:
The Bible is a complex set of books, difficult to read and understand. It should be read as instructed by the Church, and in the light of the overall teaching of the Church. Otherwise, puzzlements like yours over slavery, pork or Hell will be overwhelming and little or nothing good will come of your reading. Unfortunately, Protestantism encourages indiscriminate and independent reading of the Bible, and many branches of Protestantism tend to prefer literalist interpretations even when it is clear from the context that a literal interpretation is not appropriate, and thus they exacerbate the confusion. The result often is the conclusion that you have reached, that Bible is approximate or Hell should not be a serious concern for all men. This is a loss of Christian faith in general, not only a loss of Catholic faith. While I can only speak as Catholic, please do not take this as an attempt to convert you to Catholicism; I am attempting to convert you to Christianity.
What are the rules of reading the Bible? Like any text, divinely inspired or not, it should be read with knowledge of the context and the culture of the man who wrote a particular book. We need to look at the intended audience and the reason it is written. Besides universal teaching of Man in relation to God and to other men, the Bible contains engineering, medical or agricultural advice, highly metaphorical poetry, historical and genealogical accounts, and what not. It is natural that habits, customs and knowledge of the day will enter the narratives, and they will not be always sound social practice, science or engineering. This does not make the Bible approximate, -- without these narrative, poetic or metaphorical components it would not serve its purpose and so it would not be inerrant!
Second rule is that when the intended meaning is in doubt, one need to check how the intended audience of the day understood the passage. This is why the Catholics and the Orthodox insist on testing the understanding with the early Church fathers and oral tradition. For example, the early Church clearly believed in Hell as a real danger for many -- not just for criminally guilty -- so if you interpret biblical passages differently than that, you are not interpreting them right.
Thirdly, the Old Testament must be read in the light of the New Testament. In particular, we see Christ teaching us to read the Jewish law critically and to use reason. He repeats parts of the Jewish law making it our own, but He does not repeat all of it, and He often reinterprets the Jewish law differently even when he seems to approve of it. Later, the apostles decide to rescind parts of the Jewish law that deals with diet and ceremony. This does not point to the errancy of the Bible, merely to the fact that God gave some of His law to the Jews, and other parts of it to us Christians, and some laws pertain to certain historical epochs, while others hold for all eternity.
A few specific concerns you mention. Pork was prohibited to Jews alone, The Jewish rabbis always interpreted the prohibition not as a pragmatic one, to do with properties of meats, but as one teaching people that God's law is to be obeyed irrespective of reason. This is why Jews don't eat pork today, even though it is perfectly safe medically speaking. The dietetic laws of Moses were lifted by the Early Church because we are under new covenant and the old one simply does not apply. It was not lifted because the Apostles invented refrigeration.
Slavery is either mentioned as a fact of life in the scripture, or charity to the slaves (along with obedience to the civil laws) is urged. Or it is used metaphorically to illustrate the fact that to God we are not unlike slaves. If you have a specific passage that you think condones slavery expressly, show it to me.
Hell is punishment for sin, and the cardinal sin, as is clear from the Fall of Adam story, is disobedience to God. But Christ asks us positively very difficult things, -- to be like Him, to follow Him disregarding all else, and to give our property and lives to others. So, one who merely lives a good life, -- does not steal or murder, -- cannot be assured of salvation. Here the Protestant beliefs differ somewhat, as they would say that one who has professed faith in Christ can be assured of salvation, and we say that while this is so, works of obedience and charity need to prove that faith, and so presumption of being saved is sinful in itself. But no Christian tradition teaches that good life without faith is sifficient to avoid Hell.