This is where you run into issues regarding fungibility. I would suggest you give this video a watch for a better explanation on the topic (https://www.youtube.com/watch?v=VuI-8EwqIS8).

Also, if we were to apply this same logic to physical currency we would have to revoke something near 90% or more of the physical currency supply. (http://news.nationalgeographic.com/news/2009/08/090816-cocai...)