The theoretical benefits to society from distributing people's IP for free is that people who otherwise couldn't afford the money for a book or song or piece of software are able to use it.
Of course, it becomes impossible to support yourself as an indie producer of (software/music/literature/etc) in a world where your work can be taken for free. That reduces the number of people who can participate in the creation of that sort of thing to hobbyists and large businesses that are capable of protecting their IP through other avenues.
Getting rid of intellectual property rights is a short sighted exercise and all you end up doing once you've run through the trove of contemporary and historical IP is impoverishing the world to a much greater degree by destroying incentives for creators to create new things.
The only solutions that I've heard defenders come up with is some version of <hand waving> "it doesn't matter, people will still produce art" Yeah, people will produce, but like 1/10th what they could if they can't make a living off it or aren't trust funders.
Current copyright is life of the author + 70, which is too long. Still, even in that situation, those who wouldn't otherwise have access to those books will eventually get it for free as works enter public domain. If you want to argue that we should drastically reduce the length of copyright, I'd agree with you. But pretending that IP theft doesn't matter is naive.