Good for them.
Now, I don't want to be misunderstood. I am not advocating the use of cocaine. Cocaine -- especially crack cocaine -- is a horrible scourge. But the fallout from making cocaine and other narcotics illegal is an equally horrible scourge. It does nothing but create a market opportunity for those willing to take the risk of breaking the law, and a barrier to entry for those unwilling to do so. Making cocaine illegal is nothing more than an indirect tax subsidy for drug dealers, one the Marshal Islanders have decided to avail themselves of. And they arguably deserve it:
The Marshall Islands were the site of nuclear testing prior to independence from the United States, and Marshallese claims against the US in regard to the fallout from the atomic testing are ongoing.
Don't buy your plane tickets just yet though. This is almost certainly nothing more than a bluff to try to get draw attention to their plight and maybe get a bit of leverage with the international community. But I predict that before long (10-20 years) we'll see other island nations trying similar tactics as the gravity of their situation becomes apparent. It's going to get ugly. Civilization depends on at least the perception of everyone having something to gain by playing by the rules. When your country is sinking beneath the waves that proposition becomes a very tough sell.