At least you have a set of codes as proof that it exists.  Though Bitcoin is virtual and not tangible, you can use your sense of sight to prove its existence.  You can check and verify the program used to run the system and use your logic whether it exists or not and not rely on someone on the internet to decide for you.  You can also use the marketplace of its existence and countries' reaction of it.  You cannot ban something or approve a regulation accepting it as a mode of payment if it does not exist.

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Bitcoin is a set of codes, a script that enables a borderless P2P electronic cash transfer that does not need any intermediary such as financial institutions.