This is not a failure of bitcoin. Suppose you had a stack of companies whose purpose is to store your physical gold and prevent it from being stolen and to serve as an exchange allowing customers to trade gold for currency. Then, it turns out that some of them had inadequate security or were outright crooked and the gold they were storing went missing. This would not be a failure of gold itself. Sure, if sufficient quantities of gold were affected, it would affect the price of gold, but it does not change gold itself. This is the same situation.
Even if you stole an amount of gold equal to all of the gold allegedly in Ft Knox, or that allegedly used to be in Ft.Knox, unless you put it on rockets and send it into the heart of the sun, the world wouldn't treat the situation as one in which the amount of gold in the world already removed from the ground had suddenly changed.
The whole point of stealing it would be to exchange it for something else, either directly for goods or services, or for some country's currency to be spent for goods or services at some point.
So the world would continue to consider that stolen gold part of the overall "supply".
So stealing it wouldn't really make it less rare or more rare unless you could steal a considerable majority of the gold in the world and "corner the market", so that by keeping it out of "circulation" you cause the same amount of demand that existed previously to wind up chasing a smaller supply, which would drive up the price, but you'd have to keep it out of circulation to keep the price high, because once you start to unload it, you've increased supply again.
Not to mention that a sharp increase in the price of gold would result in a boom in previously unprofitable mining operations, which would start adding to the world-wide supply, which would bring down the price.
The real problem here is the notion that bitcoin is a currency. It really isn't. It's a virtual commodity much like gold, with similar properties save for the fact that gold is physical and bitcoin is not. (Sure, the odds that everyone suddenly decides to pack up their toys and ignore bitcoin are much higher, mostly because there are no "real" uses to bitcoin, unlike gold which has actual uses other than being somewhat "rare" and looking pretty.) The same things that make gold less than idea as an actual currency (or a backer to a currency) apply to bitcoin. Sure, you can use either one as a place holder in a transaction if both parties agree, but you could just as easily use a common fiat currency, chickens, or grains of sand.
The other day the Netscape guy explained that bitcoin is a distributed ledger system, and it seems to me that that is where its real value lies, since apparently even if it gets stolen there is a record of it having been stolen so that you don't wind up with a situation where, if all of the bitcoin in existence were stolen, it would appear that it was still where it was and you'd suddenly have twice as much bitcoin apparently in existence as was previous to the theft.
In other words, supposedly the way the keeping track of where each bitcoin or fraction thereof is prevents the creation of counterfeit bitcoin and the resulting dilution of value.
But none of this is my area of expertise, and I admit to the very distinct possibility of being wrong.