Why would we need proof of innocence? If someone robs a store do you need to prove you are innocent or do they need to prove you guilty? A similar analogy would be me out with a friend, and they walk out of the store with an item in their cart that was missed by the cashier. There is no evidence anyone was trying to steal, and if they were, how am I guilty of anything? Now add in that someone noticed it and the item was paid for before we left. It becomes a non-issue.
Why are you comparing a fighter intentionally taking steroids to GSP who did literally nothing?
The incident led to a change that should have already have been the norm. Because even if you do not intend to do anything wrong, the system they had in place would lead to it happening.