It's not just drugs: any point where regulatory or market conditions create enough suboptimal conditions (ie demand), there will be a possibility for arbitrage by taking the transaction outside of that market. Weapons, people, oil, real estate, and such will constantly create this possibility over time.
The tinkerbell effect - ie money has value as long as everyone believes is has value - is combined with real economic value creation. BitCoin is a 'bubble', and is 'worthless', and is 'meaningless', but BitCoins or some BitCoin competitor will have value as long as that potential for arbitrage exists.
Legalize drugs, weapons, fake passports, money laundering, unregulated international trade, and smuggling and BitCoin will have no value. As long as those things exist, and the tech exists, the global market will demand some kind of grey currency, and keep its value relatively high.