I'm going to agree with zeke; Good, evil, and morals are subjective. Without an objective description it's hard to place the words on a single circumstance.
WingedGod, yes it's generally accepted to say killing or murdering is bad, but each scenario is different as zeke pointed out. This applies to all other situations as well. I could take it to the other extreme and say it is right to kill someone if it saves others. Because in most systems, saving 2 or more is worth killing 1. (of course this depends on the person or people)
To respond to OP, what you're saying makes sense except for the last part; people do change based on other peoples opinions and actions towards/against them. Everything we do is in response to something else, cause -> effect. It isn't that simple for the human mind or human actions but that's essentially what it breaks down to.
So, the "morals" people speak of would be something along the lines of making rules based on how people respond to certain actions.
To bring in the example from earlier, not many people want to die, so we've made killing or murdering "wrong".