Well, this is the thing, it is pretty much a physical law. Information is nonrival: it is infinitely copyable and anyone can use it without reducing access to anyone else. The effort and work to produce information is a scarcity, but once the information is expressed and public it is an abundance.
The whole of the ethics and economics hinges upon this basic physical/logical structure. This is the fundamental fact of the matter, and if it is followed through rationally, all of the normally assumed ethics of copyright unravels.
Paying people for work done to create makes sense. It makes an 'economic' structure that mirrors the basic physical constraints. And it is justified according to its 'economic' effects. You give something up, you get something in return. The individual transaction is fair and square, and the global outcome is a gain from being able to 'move' things around.
None of that much holds for paying for copies. The transaction is not fair and square, it is an unwarranted and unjust restriction of personal freedom of those using the information. And as for the global gain, it seems rather lacking grounds of actual evidence.
> The same holds true for everything, even for murder.
No, there is something of a difference. Murder is outlawed not arbitrarily, but because it is something we do not, in a very basic way, want. It has a grounding in the physical facts of what the act does, and in the physical facts of our reaction to it (as a victim). That physicality gives it an unparalleled strength as something we all agree on.
Copyright has no such physical grounding. Would murder be just as wrong if it could be done without actually killing anyone? You do the same things, but the actual effect is not there? -- perhaps imagine it as a video-game. It is a very different thing. And this is like copying: on the fundamental level it is 'stealing' without the stealing (i.e. not really stealing at all) -- because the basic relation involved is abstract.
Etc.