That indeed is worrying, and this is why Bitcoin will always be a safe. If those people had gold, they would have no faith, but Bitcoin actually permits to track the bitcoins. Yes I have to agree it will be hard, but always possible.
I feel like all it really takes to make it untraceable is a mixer. I don't know if I'm wrong about that, but it seems like mixers would just keep the anonymity for whatever the small transaction fee is. After that, the coins are basically untraceable and that defeats most of your point. Like taking gold and leaving with it, a robber can take bitcoin, make the transactions anonymous through a mixer, and leave with the money.