Private ownership of things made by people is perfectly reasonable; the person who made the thing should own it and be able to sell or transfer it as desired. So a rock you found isn't made by people, so yeah, but a painting, or a chair, etc, was.
It's land that wasn't made by people where private ownership gets really ridiculous.
I can relate to that, but even in this manner, most of the goods made are the result of vast investments of time efort and money of lots of peoples over decades, just for few individuals to be the owners of.
It is true that once production of an item becomes a greater task than simply the work of one person, the ownership of it can be considered more complex, but my point was that at least something created by people makes sense to be owned by its creator.