Your friend writes a novel. They've never been published before, so they shop it around to various publishers, but no dice. A little while later, they see a hot new entry on the bestsellers list, and surprise, it's their novel word for word - one of the publishers took it.

Without copyright this can happen to writers, musicians, film creators, artists, and so on.

There should absolutely be limits on copyright. Disney should not be allowed to turn the copyright laws into their own personal tool. But I see so many people who get angry when corporations take advantage of copyright, and so few of them seem to consider the fact that the same laws protect the little guy against those same corporations. Unless we want Disney to literally be able to get away with stealing art from anyone and everyone, we need intellectual property laws.

As for patents, the general idea behind patents is that in order to get one, you need to describe your technique. The motivation is furthering shared knowledge - we give you the promise of exclusive use of the patent for a limited time in order to encourage you to divulge your invention. Patent law is more ripe for abuse than copyright but its general policy motive is still sound.