Except that you wouldn't get much legal protection if someone runs off with your bitcoin. A bitcoin transaction is irreversible and unfreezable, so there is not a lot the bank or legal system can do to try and retrieve stolen funds. And there is less of a trace to who the thief is.

As a result you probably aren't going to get the government failure guarantees on bitcoin as you would for fiat. Let alone governments wont want you using a different currency that they can't print.