The world's currency isn't ever going to be 100% bitcoin. It's an invalid basis to start from.

I kind of see what you're trying to hint at, but it would be helpful for discussion if you could think of a more persuasive example.

(It may be difficult though, because it seems true to say that if Bitcoin starts becoming a significant fraction of the world's GDP then it's fine if it uses a little power. Where "little" is relative to the ratio of BTC's wealth vs the world's wealth, vs BTC's power usage to the world's power usage.)