I agree that fiat only has value if a government, or some other group with capital backs it.
Cryptocurrency is distinct from "digital currency" in that it's decentralized, and not managed by a large actor. Sure, they may be doomed to fail.
Libra is NOT a decentralized currency, and thus does not deserve any support from Bitcoin/cryptocurrency people.
I 100% agree with you, just want to make the distinction between "cryptocurrency" and "digital money". Libra is Snapchat Cash + Facebook's own currency and we shouldn't try to defend it, when it is obviously trying to circumvent government regulation.
Now, it sounds like you don't think digital, private currencies/securities should be regulated. That's a more interesting conversation. Recall how the 1907 financial panics (and the Great Gatsby era) led the U.S. to government-regulated central banking in the first place.