Some morality issues are universal; others are created by different religions. Stoning is still legal in some ME countries. It is a "mortal sin" for a Muslim to convert to a different religion and the punishment is death. I do not see how any religion deals in "absolutes", since mores change over time. No longer are people burnt at the stake; the Inquisition is gone. Many Catholics differ with the Church on some matters, yet consider themselves good people. So it was in the past. THe world is no longer flat and Galileo has been forgiven.
As for "mortal sin", look up the Church concept of the "Internal Forum".
http://astro.temple.edu/~arcc/marriage.htm
one paragraph of a reasonably long article:
"The Fathers of Vatican II described our Church as a pilgrim Church. BY that, they meant that we have all had to make our way through history, sometimes proudly, sometimes painfully, sometimes striding, sometimes limping, in a not always successful effort to follow the Gospel. THe war-making popes of the late medieval era and the early renaissance limped very badly indeed. Some led lives of luxury and licentiousness, building palaces for their mistresses and handling on the overflow from Crusade treasuries to their illegitimate sons and daughters. Let those of us who never limp cast the first stone."
The ultimate result comes between the individual and the Creator. That is the only thing in the end that counts.