You are basically denying the existence of moral absolutes. If that is true, then why, in almost every single context, raping and killing is wrong. Surely that kind of occurance suggests that there is something about rape and murder that makes is simply wrong?
Wrong in, I daresay, the majority of situations. But when placed into a position whereby you see another action as being worse, as in your thought experiment, then how can you place such a confident judgement?
Here's my definition of a moraly good action - a situation where all choices considered, you make the most rational decision. And I think this leads to another one of Blue's threads.