People say that because they don’t know what it feels like. Basically, they’re projecting
Technically one can argue fairly that it doesn’t exist, but that argument would be about semantics. Doing something good for others at the expense of yourself either because it feels good to do, or because somewhere in your brain you think there will be good karma or a celestial reward, well… maybe those aren’t truly “altruism”, but can anybody tell the goddamned difference in the grand scheme of things?