I like to look to this quote to help with understanding the initial purpose.
"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"
The phrase indicates it was not giving them time, because they had the rights to it, or because they have the right to success as a result of their ideas, but to only promote progress. Science and Arts, but in the nature of progress.
I like to imagine if there were no limits, and that once you created something, it was yours forever. Saying this is the case, the Inventor, or more appropriately, the party who patented/copyrighted the work first, or something else which can say that a future work was derivative of, was in fact entitled to the person who initially filled our the form.
This being the case, you would have industries of single companies all the times. Monopoly after monopoly. Jim invents the Pencil Sharpener, and after that, Jim has the exclusive right, and perhaps his descendants after he leaves us, to make Pencil Sharpeners for so long as there is a need for them. This does not promote competition within the same field, but only in that someone will try to find a simpler solution, that they can copyright themselves. Also it can lead to monopolistic tendencies, from Price Gouging, to forcing competitors out of the market.
I'm sure some companies wish they were the sole manufacturer of their product, as it may be better for them, but it is worse for the market, and worse for people overall.
In the Arts, you would never hear a cover of a song if it was similar to the above idea, for someone who would choose to lock down their work. People learn to make their own music, by learning to play music first. Imagine if they could only play songs they purchased, or have a right to play, because they needed to purchase it. It discourages people to learn and respect the art of others, to the sole creation of their own. I can foresee owning a Genre, if the above were true. A genre gets started by many people doing similar things, but image for every song they create, because it is in some way similar to a prior idea, that they need to be paying out to that owner?
Of course it would not be restricted in everything, people would license their works, genres, and machines out, and that cost would be pushed the the end user in turn.
Admittedly I do not know a lot about Medical Science, but I'll use a Wheel Chair as an example. Now at first you would think, it's just a chair with wheels. Say Wheels & Chairs have been around forever. But handles have not, and are copyrighted. You have to pay that to the Content Creator. Also the foot rest and the brakes are also fairly new, and those need to be payed for as well. Those costs are payed out, and the Wheel Chair price goes up.
That seems contradictory to the initial intent to Promote the Progress, and in turn hurts it further.
A far worse thought than the above, which is not too far fetched from our current though, is the Patent Troll. In that above world, say companies would just exist on buying patents for people, hoarding them for a day when they would serve them better or when they can be combined. "It's not a lot of money coming in now, but in time, small mirrors will be built on every car, and there will be a premium paid to us, so that they can still build them. We can tout safety and awareness, and why the need to be on every car, and people will then have to pay us."
In this fictional society, and our own, in the long run, there would be few companies, who own patents on everything, and would fight against the other companies who came up with an idea, or try to say it was derivative of their own works. They have no incentive to do more than they need, and in all likeliness they would have far more lawyers than engineers.
Imagine in that world, if Copyright was eternal, their work their own, if people were working against human interest and progress, and banning people from things that would improve their lives. Already we see it now in medical science with the patenting of drugs, devices, and no doubt in time procedures, that companies feel entitled to, and is not for the progress of man.
Where Copyright could help is in flexibility. Certainly you want people to keep innovating, as the purpose is to give them that amount of limited time is for them to succeed with it, and in turn, to move on to something else. It was not because they had a right to their work or to succeed, but because they wanted people to keep innovating. We praise people who continue, the names of Edison, Tesla, & Bell are remembered because they did so much, not because they had one idea, and spent their lives milking the money out of it.
Progress being the goal we strive for, and to push further, incentive should help, and copyright could be used for the better. We want the inventors of the world to keep inventing, the song writers to keep writing, and we want to progress as a society. No one debates people should be able to capitalize on their own works, or even if they improve on another persons work, but it should not last forever. It should not last longer than it takes to put something into production. Some things will take time to bring to market and will require preparation, and the ability to do so. Things invented today are not seen for years in homes. But once production occurs, and it is on the market, is it not fair for another to compete, much less improve on someones work.
Take a computer mouse. Single button, Dual button, and in time the scroll wheel. Though we applaud the invention and it's ease of use, if in time someone improves on the initial design with their own work, do they owe it to the originator so much, to restrict the progress in the nature of personal gain? Sometimes competition hurts the market, and this is understood, and if there were better ways to cooperate, perhaps it would not be such an issue. However even cooperation in this day and age, can invite legal troubles. Companies force you to sign the rights away to all things you create when you start for them, not just for their own greed, but also to limit liability and competition should someone go elsewhere.
It would be cheaper for business to not have to prepare for lawsuits on frivolous copyrights, it would be cheaper for the end user to not have to pay so much to everyone who is owed when a product is purchased. It would assist in competitors coming to market with alternatives. The Gucci knockoff purse sold for 50$ rather than full price, does not devalue the Gucci brand, but increases it, in that another has to lie to sell their products. And if the initial product is better, it should sell better, not because of brand, but because of quality.
I feel competition & cooperation is better for Industry and the Arts, and both are better for the progress of mankind. Restrictive copyright hinders the options of both, regardless of intention, whether they forestall changes in their industry, or the protection of intellectual property. Where are our the new generation of Libraries in this digital future, to grow and learn in? We imagined computers, not in the classroom, but replacing the desk, the text book, because it would be more efficient, save paper. What happened to the paperless office? I don't think copyright killed the ideas, but it took far longer for a book reader to come out to market in a push from Amazon, than it did for most every other type of media. The industry that will be last to fully arrive in this digital era, is reading one, and yet books are the smallest size. One High Definition movie's worth of space on a PC could fit probably every text book written in the last 30 years in the same amount of space.
The way it is used now is causing stagnation instead of creativity and advancement. Restrictive Copyright is now used as a weapon, to fight or scare into settling lawsuits, or to quit entirely. And when I'm using the words fight and scare in a sentence, I'm thinking the last thing on your mind is the word progress.
Just an observer.