Burning fuel for NASCAR and Formula 1 is also useless to a first approximation, and surely the land used for racetracks could be used for other stuff. But millions of people find it entertaining, and occasionally useful stuff comes out of it, like innovations in engines or telemetry or safety equipment.

How is this any different? It's entertaining plenty of us, it's less fuel than a race and less land than a racetrack, and maybe we'll learn something in the process. Maybe innovations in moderating the futility of online comment systems. ;)