It has been demonstrated that:
1) gold can be stolen due to mistakes
2) bitcoin can be stolen due to mistakes
but this does not mean that it is impossible to avoid having either stolen.
I agree that long term storage of both of these can be done very securely, but the risk for both is when trading or using them. Additionally, Bitcoin does require a lot of worry about security - how many people do you think have airgapped wallets?
Aren't the facts that you shouldn't store Bitcoin at exchanges, should use an airgapped storage mechanism, and are otherwise out of luck if your computer is compromised, enough to demonstrate that you also have to worry a lot about the security of Bitcoin transactions? Your stack of gold ingots won't vanish if you take one from the pile in your safe, but your Bitcoins can if you don't take stringent precautions.
If you view a Bitcoin transaction as only what happens on the blockchain, you're missing the context of where it occurs - which gives both gold and Bitcoin risk.