But if there are moral absolutes, then capital punishment, slavery and torture should be absolutely right or absolutely wrong. However, they are not. So why does not this prove conclusively that morality is not absolute but varies depending on the culture and the times.
You’ve probably heard of the non-negotiables regarding moral issues that were often spoken about or written about before the election in 2008 and other times too. I know that abortion is one, euthanasia, homosexual marriage, cloning, embryonic stem-cell research. These are related to specifically pro-life issues. They are absolutely wrong–inherently evil-- in the highest sense because they are like a slap in the face to God our Creator. Other sins relate mostly to our neighbor although they still offend God. Murder is objectively and absolutely evil since it offends God and man. Even Spock agrees. However, Jesus enhances the prohibition against murder saying,
“You have heard that it was said to your ancestors, You shall not kill; and whoever kills will be liable to judgment. But I say to you, whoever is angry with his brother will be liable to judgment.”
Therefore, hate and brutality of any kind are anathema to God. As a Catholic you’ve probably heard of the seven deadly sins: gluttony, pride, lust, anger, greed, sloth, envy.
They are also called Cardinal sins. Captal punishment, slavery and torture (meaning the kind used by authorities) are not subject to the individual but to the state, the government, society, rulers, and even though they are probably objectively evil/morally wrong, it is likely not personally sinful for the individual (like the person who gives the injection for capital punishment or the slave owner or the authority who does the actual waterboarding, for example,) since these particular evils were cultural institutions. (Actually, the Nuremberg Trials reduced that argument saying that any participant in the murders could not use the excuse that he was just doing his job). Nonetheless, an individual can become a proximate cause of the evil by deliberately increasing the pain of the person being punished. Also, you’ve got to think that at the time of slavery, many of these slaves were well-treated and some didn’t even want to leave their masters when slavery was finally declared illicit. Some didn’t know where else to go or just couldn’t make the transition.
BTW, all I can do is relate things as I’ve studied and read but to get to the nitty-gritty of your question, it might be best to add it to the forum as a separate thread. There are some good philosophers and theologians around here.