I disagree. I think it's more like being a vegetarian. You can happen to not ski, but at least in a First World country, it takes efforts to be a vegetarian. Most humans eat some kind of meat and have an instinct to seek meat out. And some vegetarian still crave meat, so they come up with artificial foods that look at taste like meat even if they aren't. Most atheists I know believe in something bigger than themselves that they derive their identity and self-worth from. I think humans crave that like they crave meat. You don't have to indulge in that craving but the instinct is there. Agnostics that don't observe worship ceremonies. That I think would be analogous to not skiing.