People should be rewarded for their mental labor, but that’s not the same as saying they have created intellectual property.
A thought or concept is not an object that can be stolen. An idea cannot be a scarce resource that is used up.
If concepts or ideas can be “stolen” then that means somebody is being deprived of them. But unless you somehow erased the idea from all parts of that person’s brain and transfered it into yours, nobody has been deprived of anything, and thus nothing has been stolen.