[zucker42]

If you have a successful bed making business, and I decide to start making beds too, you'll certainly make less profit, but I haven't stolen from you. Deprivation of income is not theft, practically any action you take deprives someone of income.

Most justifications for property (both personal property and real estate) invoke the fact that pieces of property are rivalrous (one person's use interferes with another's). Calling unlicensed copying "stealing" ignores the crucial difference between physical goods and digital files.