Kind of depends which angle we approach it from. Someone does have to first purchase the game to get a DRM free copy to make (legal) copies to share. It's not really stealing outright, and publishers understand that they're giving their customers the option to share their games with others when they sell on GOG.

In this view, then it's kind of like paying it forward. Those who cannot afford it can use it for free. Those who can are encouraged to pay, get their own copies and pass it along to others at disadvantage, like sharing infinitely replicateable books.

Admittedly it's a more optimistic view assuming most people would do that. But, if pirates pay for Stardew Valley, it means there are people who abide by this.