If I may go into a slightly related tangent for game devs.
Some game devs spend a lot of time and money trying to prevent people from modding their games. Some game devs make it easier to mod their games or even encourage it.
If a mod gets popular and gets a community growing around the game - is it doing good or is it doing harm? Assuming that a large amount of the community growth is from people pirating the game to play the modded version (and assuming none of the above server issues)
There are 2 sides with difficult-to-measure metrics.
1) Is the mod and the pirates playing it bringing enough attention to the game and free publicity/advertisement as to onboard new paying customers?
2) Is the time and money spent on preventing such a mod community from growing going to cost more than potential "lost sales" of pirated copies of the game? In addition, what is a "lost sale" and how are they measured?
To expand upon the issue of "lost sales" a bit:
Plenty of pirates argue that if they could not pirate a game - they would not purchase it either. I fall into this crowd. Outside of the stupid amount of money I've spent on League of Legends, I've only spent money on games I originally pirated. I purchased the game, purchased DLC, or purchased merchandise related to the game. If I could not pirate the game - I would not bother playing it, telling my friends to buy it, or buying merchandise from it (since I wouldn't know I liked it!)
By allowing people like me to pirate you actually win an otherwise lost sale. This is what makes these metrics so hard to quantify. Too many game studios consider all piracy to be a lost sale when people like me are the exact opposite. Without piracy we would have been a lost sale.
So it comes down to "which game studio/game dev do you want to take their word for?" Many of them attribute their success to piracy of their games. Some of them say piracy killed their game.
Without quantifiable metrics... how do we know the "killed games" didn't die simply because they were bad games that, piracy aside, nobody wanted to purchase?
From a business perspective, that's the far more likely scenario than the good games that the game devs claimed piracy helped selling well regardless of piracy because ???
TL;DR
My argument is that piracy doesn't kill bad games due to lost sales. They don't get any sales because their game is bad and few people are willing to pay for it. On the contrary, popular pirated games still do amazingly well because they are good games that people are willing to pay for even with the availability of pirating. To myself, makes more sense from an economic perspective for gaming media.