Same reason I don't want to have dinner in a restaurant next to someone trying to cut their steak with a chainsaw: at best they are being incredibly obnoxious, at worst they are going to maim me. Just because it is better for your once-a-month weekend lumberjack trip with the boys doesn't mean it is an appropriate one-size-fits-all cutting tool for day-to-day use.

Contrast that with someone having a needlessly powerful computer. How does that impact the rest of the world? Not at all, it only impacts the owner's wallet. Someone's needlessly-powerful computer has never killed a child, or taken up four spots in public. Heck, it'll even downclock when idle, so there isn't even any extra power use to be worried about!