But there will be a chance that is can disappear because the value will go down or something.
Bitcoin is decentralized and the market is a true market. True free markets without intervention will be prone to ups and down, but the overall trend has always been UP. Everytime bitcoin crashed, it set a new floor.
Neither is true. Bitcoin has long ceased to be decentralized, and I don't really see why severe market manipulation cannot be called intervention of sorts. At lest, interventions usually aim to stabilize the markets (i.e. make less volatile), not to shake them either to boost the price up or crash it down. If you question the latter (i.e. market manipulation), you should first refute the former (i.e. Bitcoin centralization)...
Since manipulation directly follows from centralization
Bitcoin is not decentralised in the sense that ownership of coins is very unequal (someone should measure a Lorentz curve coefficient, actually), but I believe it very much is in terms of hashpower (as a cursory look at the block signature estimates of Blockchain.info would reveal), so it is important to get our terms right; perhaps the poster referred to the mining power. Even if it is the ownership and it is rather centralised, that does not mean that market manipulators have full control. It is limited by those that hold their coins untouched in places due to legitimate economic activity, or have simply forgotten about them (c.f. Satoshi himself, for one)
No, I didn't mean wealth inequality. I assumed myself that the poster referred to the mining power as a representation of Bitcoin decentralization, while in fact it is severely centralized. I'm also looking at the hashrate distribution estimates given at Blockchain.info, the screenshot of which I just made and insert below
By any means, I can't call Bitcoin mining power decentralized. Now we have 7 major players which swallow up about 90% of all hashing power out there. What is it if not an example of extreme centralization? If we consider Bitcoin as a global currency, then all major fiat currencies taken as one will be more decentralized than Bitcoin