A combination of factors makes the bitcoin currency very crash resistant.
A crash would occur under a mass sell out. Considering a very significant event that undermines the security of the bitcoin system would have to occur for a mass sell out to be rationally justifiable, such as a government or other powerful group/individual spends massive resources to break the system, a hacking or some form of take down on mtgox occurs that involves many losing their bitcoins, or some entity creates a quantum computer capable of breaking the SHA256 encryption in reasonable time and starts targeting bitcoin accounts, I think it’s safe to say with a very high probability (at least at the current state of events) that a mass sell out would occur due to snowballing speculation/panic selling combined with or initiated by large investors getting their bitcoins out.
Such a mass sellout will happen from time to time due to natural market movements. However any massively significant crash, such as going from 30$/bitcoin to