There's a reason for this. Me? It's in my marked interest, as it is for anybody who works within and stands to benefit from the current system, to keep the debate firmly on grounds of morality. Because, barring a change to the system, it's not only an extremely easy argument to make, but it represents the last available appeal to people who would otherwise bypass that system entirely at the expense of a few distant actors.

That's also a valid answer to the original question - "You really can't". I mean, perhaps it's not the most useful of answers by itself, but with your added explanation about the course of action people like us should be taking, it does still contribute to the discussion.

It means that people like us will just have to keep working at changing that system - to show consumers and creators alike that you can still be compensated for producing content without copyright.

You're going to have a hard time refuting it, too. On the other hand, if you as a file-sharer take up the argument on practical grounds, your job becomes easier: "whether or not my actions are moral is moot; available technology allows me to assign lower monetary value to the stuff I want. The onus doesn't fall on me to ignore available tools, it falls on the market to correct for the presence of those tools."

One of the reasons I asked about this problem in the first place is because framing the copyright debate in terms of morality is a political move as much as it is a rhetorical one. Somebody who espoused the above argument would be summarily dismissed by copyright proponents as a selfish, amoral sociopath.

On the other hand, as a creator who believes in the culture of sharing and remixing, I'd say that adopting the existing copyright system for small periods of time on some of my own works would be favoring pragmatics over morality on my own part.