Here is the entire legal basis of patents and copyrights in the US Constitution:
"To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."

It is very clear about the reasons for them: "To promote the Progress of Science and useful Arts..."
and the means: "by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
Of course one can argue that the means don't meet the purpose today or that the limited times are not so limited, but this is where it all starts.

Regarding "Intellectual Property: I dislike the term intellectual property because it isn't really so much property as a government granted monopoly and it is overly broad. There are astonishingly few cases where one needs to discuss patents, copyrights, and trademarks as a single thing. They are more dissimilar than similar. IP is like discussing how to regulate birds and airplanes under the term "air traffic." Sure they both fly, but one would hardly want a uniform legal system for both birds and airplanes. (Should we fine birds for not getting proper pilot's licenses? Or should it be the responsibility of the municipality or the local birdwatcher association to get licenses for the birds to fly?) None of these questions make any sense unless you're thinking of both birds and planes as "air traffic". Patents !~ copyrights !~ trademarks.