Why some Christians would follow situation ethics
Jesus seemed to follow situation ethics because he over-ruled what the Old Testament said when he thought it was unloving. For example when a man with a paralysed arm asked to be healed on the Sabbath Day, Jesus healed him because he said it was more important to do good than to obey the low not to work on the Sabbath.
They think it is wrong to ignore the consequences of your actions. You should only do what will produce good results. So they would steal the nuclear weapons and allow the twelve year old girl to have an abortion.
They believe that Jesus' statement, that the only laws are to love God and love your neighbour, means that Christians should always do what will have the most loving results.
Why some Christians think situation ethics is wron
They think God would not have given laws in the Bible if they were not to be followed
they think the Church knows better what Christians should do than the individual.
They claim you can never know all the facts, and so don't know what the consequences might be. For example, what if a doctor in a remote area only has one unit of blood to save the lives of two people. Following situation ethics hw would use it fr the mother, but what if he then learned that the mother was a child abuser and the old man was about to discover a cure for cancer? the situation would be changed and he would have been better to follow Christian teaching and to have given them half each.