But you're still ruining other people's fun for selfish reasons. Why not find some fun activity that's not a zero sum game?

The type of cheating I do rarely interfaces with other players, outside of enriching them with the spoils of my effort when I'm through. In a protracted way I can agree this "ruins the fun"...but not in the way that griefing does. I just spike in-game economies and leave. Balance is shortly restored.