The main idea of utilitarianism (U) is to create ‘the greatest pleasure for the greatest number of people’. This is similar to Christianity and the golden rule ‘love your neighbour as yourself’. With situation ethics, in a dilemma you should always do the most loving and compassionate thing. However in contrast to the utilitarian idea that you should try and greatest happiness for the most people, Christian ethics would look at everyone in an equal manner, as everyone was made ‘in the image of God’. It says in the bible that God is personal and loving and therefore looks after the vulnerable, whereas utilitarian’s would have to ignore the minority for their theory to work.
Also against U is the absolutist approach that the divine command theory, Kantian ethics and natural law hold. Christians would say actions are intrinsically right or wrong in themselves, whereas U would look at the possible consequences of an action on whether it is right or wrong. Christians believe that a consequentialist may justify evil acts, and it may not be the most loving thing to do.
Another way U is different is that it ignores the sanctity of life, and focuses on the quality of life. For example if a pregnant woman was told her child would be severely disabled, and would not live for a long time, Peter Singer would say the best thing to do would be to abort it, as the quality of its life would be very poor. However Christian ethics would say God made all life sacred (‘God made man in his own image) and therefore the baby shouldn’t be aborted.