The US government forces US citizens to trade with dollars. The Chinese can take their dollars and buy goods the Americans produce. The American producer has to accept the paper dollar (that for itself has no value) because government is pointing a gun at him. Basically nothing (paper dollar) becomes something because the US government walks into the shop with me with guns and "convinces" the shop owner that I can trade Nothing (my paper dollar) for Something (his goods).
Now what can I do with bitcoin once you transferred it to me?
you can buy almost everything, do not you? what you are saying is misleading there are no cops in the shops. You do not need violence to emit currencies, you can just be a bank. If there will be, and it will, rich people owning both bitcoins and other assets in no way the value can go to 0. So it is a store of SOME value, given the rareness cyclical hoarding comes, that's a fact and depends all on the portability and safeness of this asset, which are REAL values no other asset can show. It does not matter if a btc is worth 1 dollar or thousand, it's a safe store for a million dollars wealth, that's enough. That's different from tulip mania because tulips are not inherently a safe storage, we can't say the same of all other bubbles. Paradoxically having no backing asset but just an excellence in cryptographic safety makes this bubble a no bubble or the perfect bubble, as you wish. Only security issues definitely matter.
Why exchange something for nothing? I dont care if nothing is rare. Its still nothing.