Ideas are intangible, not property, and someone can think the same thing as you without ever having met you or heard of you. A more accurate term than "intellectual property" would be a "short, government-protected monopoly on an idea". But we call it property, and after many years of calling that, it insidiously starts seeming to us like real property, and not the temporary monopoly it really is.
There's room for short, temporary monopolies. As the framers realized, copyright and patents are critical to fostering innovation and culture. Unfortunately, "short" went from being a very reasonable few years, to a slightly less reasonable 20ish years, to now, where if you publish a work today the chances of it being available to the public within 150 years are slim. Do a grandchild's grandchildren deserve to lord over something created by a dusty ancestor centuries ago?
In a strange and sad way, our IP regime today means that individual authors are unlikely to be remembered by history 100 years from now. Look at Project Gutenberg or Wikiart: hundreds of people from all over the world volunteer to lovingly scan, transcribe, format, categorize, and distribute works from the last few centuries. They do this because that work belongs to the public now, and their efforts keep the memories and impact of those works and authors alive. Do you think anyone will do the same for your work 100 years from now on the pain of legal threats and huge fines, or is it more likely it'll fade into oblivion?