Limiting letters patent to inventors and copyright to authors, as reforms in England not long before the American Founding had done, were part of what the Founders were getting at with that clause. I think they would appalled that the clause has in these latter days been used to justify laws under which a publishing house could prevent the use of a 1928 poem by a poet who died in 1968 as song lyrics in 2003. (I cite the case of Robert Frost's poem "Fire and Ice" the monopoly rights to which were held by Henry Holt & Co., who prevented them from being used as song lyrics by the neo-medieval band Unto Ashes, prompting them to replace the poem with a parody about failed royalty negotiations entitled "Flayed by Frost". The track Fire and Ice, which was released in Europe years earlier, finally was released in the U.S. in 2012.) This use of copyright -- the suppression of derivative works by publishers and literary estates -- is the antithesis of the Constitutional purpose of copyright.
The current state of the law is such that one would imagine the Founders has written a clause "to impede the progress of science and the useful arts, by securing for indefinitely extendible times to publishers and other commercial interests the exclusive right to the writings and discoveries of others."
It wasn’t until 1622 that England established copyright laws and it wasn’t until 1710 that the laws reflect much of what we understand as copyright laws.
The laws were not being relaxed in terms of copyrights, they were being strengthened in 1789 when the U.S. Constitution was being written. Jefferson and Franklin were both strong advocates of copyright laws in the colonies and later the United States.
The original length of copyrights were 14 years with another 14 to be applied for. However, throughout the 19th century, the move was toward more stringent protection of an artists or inventors works. The Constitution was not a loosening of copyright and patent laws, it was a step on the way of recognizing that people who do the work should own the fruit of that work.
And since the United States is a signatory of the Berne Convention now, that treaty has the same weight of law as the U.S. Constitution itself. (You can look that up in the Constitution. Article VI reads in part: This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land)
And where is the liberty in taking someone else’s work and making money from it? That doesn’t sound like liberty to me. It sounds like theft.