What is your evidence for these claims? Bitcoin and other cryptocurrencies go through multiple price fluctuations a day. The American dollar currently underpins and backs a majority of the world's financial system [1]. Sure it isn't flawless, but its way better than something that has no backing from anything. I would prefer to use the currency issued by the world's most powerful independent state, because they are probably gonna be around for a while.

[1] https://en.wikipedia.org/wiki/International_use_of_the_U.S._...