>It is more difficult to determine how much money is "stolen" when someone violates copyright law
You may violently disagree with this, but if you're struggling to figure out at least a lower bound for how much damage might have been done, the answer is probably "almost none".
I mean if it helps you sleep at night after you pirate a bunch of stuff sure, but ultimately there are people out there who want a digital thing and have the money to buy it. Some percentage of those people pirate the thing and money is lost for the content creator.
You may violently disagree with this, but if you're struggling to figure out at least a lower bound for how much damage might have been done, the answer is probably "almost none".