The thing is, since these exchanges operate within legal boundaries and the owners are known and probably documented by law enforcement agencies, we are somewhat safeguarded if our fiat were be stolen or abused by the owners of the exchange. There are systems in place in the real world which would combat criminal endeavours to steal our fiat. Bitcoin has none of those. It might all turn to shit tomorrow, that's the harsh truth of it all, and you wouldn't be able to do a damn thing to prevent it. Your coins might even get stolen from the exchange, and you wouldn't be able to do squat. You might be a "bitcoin believer", but i prefer to be realistic about this whole thing, and i think that's the smart thing to do as well instead of putting blind faith into all of this.