There are a few important concepts in relation to ethics, which help in such debates. For example the concept of idealism. Idealism being the belief -either conscious or not so conscious) that ideas exist seperated from the pheonomenon of their every day function and occasional appearance in one's consciousness. For example a person can be of the view that there is a set meaning of murder, along with the impression it would make to him, and that if he happens to see a murder he would feel that which murder 'is', in a way like if he happened to fall from a tall bench he would feel certain pain due to the fall because of gravity and his body mass.
However another way to look at things is by de-idealising them. The fact that it is rather obvious (to a degree) that different people have very different views, and very different consciousness as well, leads to the conclusion that we are not moving in a world that has anything set as far as impressions, emotions, thoughts go. Therefore apart from the legal distinctions about murder (which are just laws) the emotional gravity of such an action cannot be argued to be the same, or even similar, for all people.
It is very usefull that the law is against murder, since in an organised society there have to exist laws, and ultimately the law could only be against the destruction of human life in such a direct way. However the law is not a reply to what anyone specifically feels about murder.
In ancient greek mythology, for example, there had been the Herinyes (not sure what they are called in english) which were winged, monstrous creatures which appeared to murderers so as to make them suffer for their crime, and were generally personifications of guilt. In this way an abstract and personal emotion (guilt) was given a collective form, which is another form of idealism, this time in art.
But any person would be feeling something very different, and exact, nomatter in what depth he would or would not be able to examine it. That the law recognised 'murder' as a set term is only another type of usefull idealism, since the law is not part of active thought or emotion (which again is thought, but unexamined) but a system of organisation of approximated accepted ethics.
Another argument from ancient Greece is that of Plato, that people do "evil" only out of ignorance, and therefore that development of their way to think would banish that 'evil'.
In psychology, which appeared in scientific form only in the beginning of the 20th century, there is much focus on the break up of negative and positive experiences in the early years, as for example they can be seen in children of very young age who feel that they have to "return" the negativity which was inflicted on them by hostile actions of other children or adults.
