In some ways it is dated. Which is why it has to be updated once in a while. For example, to add the ability for women and minorities to vote. It's also ironic that you mention the Constitution. Considering the ideas present in that and the Bill of Rights were actually pre-existing ideas.

As for incentive, the same reason why scientists continue to do work. Name recognition. Not to mention your ignoring the fact that before patents even existed that inventions were always being created. Hell half the stuff that made it possible for you and I to type on the Internet today came from China (Compass, Gunpowder, etc..etc..). None of those inventions were ever patented. If they were then the world would be a drastically different place. So I'm afraid the *roll eyes* goes back to you. Not to mention the history of the United States (the owner of the very document you cite) benefited from not co-operating with patent and copyrights for many years.

Another problem with the patent system beside it's long duration and the inefficiency of the patent office is that each country can issue its own patents. In a era of Globalization it leads to problems like this. So who really created the idea first? It goes back to the idea of paper. It's commonly theorized that paper was discovered by several civilizations independently. You can't prove independent invention in this day and age easily since the people likely holding the patents are the ones with the money to sue you out of existence. Often it's just easier to settle than pay the court and lawyer costs.

Do I think patents and copyrights are needed? Yes. In this day and age it's also easier to screw people over (in the older days if you did that your reputation would be tarnished). Nowdays it's easy to create a new identity. But like unions, capitalism, democracy, communism, religion, and any other idea, humans have taken them far past their original purpose.