First of all, thanks for sticking to the point and keeping this discussion civil. Would be nice to have a little debate over a couple beers.

"copyright is an artificial restriction that doesn't do what it's supposed to, which is to encourage artistic works"

I'm not sure copyright doesn't encourage artistic works, but I would actually dispute that this is the only goal of copyright. I would say that the goal of copyright is for a creator of reproducible works to be rewarded proportionally to the value they contributed to society.

Consider this thought experiment: Suppose we had absolute proof that doctors would still heal people exactly as much as they do now if we stopped paying them. They would live in poverty, but they would practice medicine out of their passion for the field, desire to do good, whatever. Would it then be right to institute a system of "free medicine"?

I am inclined to think it wouldn't be right. Contributions should be rewarded, even (or perhaps especially?) if the contributor is not doing it because of the reward.

re IP: I think you support more restrictions than just correct attribution. Can I take someone's song and perform it for money without paying them, provided I credit them? Can I burn the song on CDs and sell them in a store without paying them? Can I record a concert in HD and sell streaming access to it? Can I take Microsoft Windows, crack the copy protection, and legally sell the cracked software in an online store? If not, can I distribute it freely on a website on which I sell advertising?

Notice also that a policy of free copying would introduce an arbitrary distinction. If you host a word processor on your server ("software as a service") and sell access to it, you can make money. If you sell a word processor that runs on your customer's computer, you cannot make money, because then customers will be able to legally copy the software among each other. This is arbitrary -- in both cases the value provided to society is the same, it's just that in the first case, you obscure your code from your customers to prevent copying.

Apart from the arbitrariness and, well, unfairness of this system, it would encourage centralized software provision and draconian DRM schemes (for example, people would write desktop apps in which crucial parts of the code run on some central server, so that the customer's computer never "sees" the code). This is bad for the customer -- you have to be online to use the app, it eliminates privacy, it encourages obscurity which is bad for security, etc. We'd be telling software developers: "You can make money only if nobody ever gets their hands on your code. So you'd better hide it really well".

I realize we already have some bad DRM schemes (esp. in games), but it would be worse if copying was legal. Right now copyright restrictions stop many people from using pirated software. Not so much individuals, but think about businesses. The only way for Microsoft, Adobe, etc. to make money would be to run large parts of Windows/Office/Photoshop on some central server. That wouldn't be good.

Of course software makers would still be better off than songwriters and authors -- they cannot hide their work from the world.

"if you don't think anyone changes their minds from online discussion, why are you engaging in this one"

I'm not sure. Two answers come to mind:
1. I can't stop myself when someone who appears smart writes things I consider to be false on a subject I consider important.
2. I believe (as I've previously suggested and you have confirmed) that sometimes people change their mind after the discussion is over, even if they won't budge during the actual discussion.