You’re still generating a loss of income to someone somewhere. I completely agree there are some ethical arguments in favor of piracy, but don’t be a fool, of course piracy is a form of theft. Nothing is black or white. I still do it when the legal offer fails me, but I’m honest with myself.
In the same way, going to an half empty theater to watch the show without paying would not be stealing according to your definition (you’re not taking the place of a paying customer anyway), yet it is a form of stealing too.
>You’re still generating a loss of income to someone somewhere.
No you're not. A pirated copy is not a lost sale. Many people wouldn't interact with some media/software at all if they hadn't pirated it. Linux on the desktop would probably be more popular too.
And the person stealing a seat in the theater would not have bought it so it’s not a lost sale either according to you. Maybe lost sale is not the correct term, but it’s still a form of theft: you took something even though its owner didn’t allow you to take it.
Someone sneaking into a movie theater is consuming a limited resource (a specific seat at a specific showing) and causing some presumably small amount of wear on the seats. They're actually taking something even if its value is probably significantly less than the notional lost sale. But someone who downloads a movie has taken nothing. They just have something someone didn't want them to have.
Even if you bought a Blu-ray, chances are the licensing doesn’t allow you to do that. You usually can legitimately share with close friends and family to a certain extent, and that’s it