Ideas certainly will become scarce products if people aren’t protected for having them.
Of course you can steal someone’s intellectual property. If you copy someone’s idea you are depriving that person from profiting from said idea and depriving them of income. There is a limit on how many people can profit from a given idea.
Intellectual property protects those who innovate against predatory practices. You are displaying naivety for who intellectual property is seeking to protect. By not enshrining IP in law you are literally stopping people from earning money from their mental labour.
If IP law didn’t exist why would anybody spend their time and money researching and creating new inventions if someone can come along and steal their idea?