tell me what is the value of a global scale value ledger which can only be changed a consensus of its participants and is immune to any other intervention? additionally this ledger also has a function and is scarce.
But bitcoins are not equity in the bitcoin network. Buying one bitcoin does not make you owner of a fraction of its hashpower. At any time, the bitcoin miners could abandon the Satoshi20090103 blockchain for any other coin with similar protocol that is more profitable to mine; and bitcoin owners will not have any say in it.
Units of accounting in the unspent transaction outputs in the longest branch of the Satoshi20090103 blockchain (aka "bitcoins") are indeed scarce, as long as Gavin and the miners refrain from changing the protocol; but there is a potentially infinite number of blockchains with the same properties.
If, at some time in the future, a better altcoin comes along (say, with a 0.1 second mean confirmation time, or a distributed trustless way to seize and return stolen bitcoins), and takes over the bitcoin "market", there will be no central bank to swap old bitcoins for new ones at a fixed rate. Some owners of old bitcoins may be able to sell them to suckers in exchange for new ones, before they become worthless; but many will inevitably lose the money that they invested in BTC.
Bitcoin mining is currently financed by an "inflation tax" of 5-10% per year. At some point, that inflation will stop and the miners will start to require transaction fees. No one knows how much those fees will be, but mining is already an oligopoly market so a cartel of 2-3 mining companies can set the fees to whatever gives them maximum net revenue. By the way, those fees will apply to every transaction, including hotwallet-coldwallet moves, BTC deposits and withdrawals, etc..
at this point of time the market capitalization is 0,05% of the gold market cap....
The "market cap" is pretty meaningless for bitcoin, because most of the 13 million extant BTC were never traded, or were last traded for a very small fraction of the current price; and the market has little liquidity. If all the current owners of Apple stock decided to sell everything within a month, they would find plenty of eager buyers, and the total dollar amount of those sales would be close to the market cap. If the same happened to bitcoin, the price would plummet to unpredictable lows, and the total sales volume would be a very small fraction of its nominal market cap.