Do not expect stability in the Bitcoin exchange rate for years. In fact, these people can pretty much play with anything they want, housing markets, economies of entire countries, et cetera.
When you say "currency should never fluctuate like that in a day" how do you propose we design a voluntary currency with no barriers to entry in order to prevent the insanely rich from playing with it like a cat with a mouse?
+1. There is no asset safe from the greedy tentacles of global finance, from the madness of crowds. We will have corrections and we will have crashes. You can design the protocol for the blockchain, but look around at the state of global economics. There are no experts who can engineer efficient price price discovery, in any market. It is what is it, love it or hate it.
I have learned to love it. Be patient, don't panic (not to buy or to sell), and you will be rewarded.
The safety lays in reality. If they toyed with some financial asset, like shares or bonds, they really couldn't make them double -not in such a short time, at least. Same with currencies. Of course they play with currencies, bonds, shares. But no one will buy a company double the price it was next month -it has foundamentals which prevent it from being vaued too high (or too low). Same with a nation's currency. Bitcoin is one of the few things in the world that is purely speculative -and thus vulnerable. It won't be any more only as soon as real world trades will gratly overpower speculators -not only the big ones, but the crowd they manipulate as well.