The "crime" = "action" + "state of mind" conceptualization is the result of the Model Penal Code (http://en.wikipedia.org/wiki/Model_Penal_Code), which is an extremely well thought-out systematization of the centuries old principles of Anglo-American penal law.
Ango-American law has always placed a very heavy emphasis on state of mind, though the Model Penal Code is more rigorous about applying the principle. However, it stops far short of punishing thought crimes, because it always requires a guilty state of mind to be accompanied by action.
As for why this is rational, think deeply about the attempted murder example. Consider A plots to murder B, and with that plot in mind buys a gun and heads for B's house. The police catch him and charge him with attempted murder because: 1) he intended to kill B; 2) he took a substantial step towards carrying out his goal. Why do we punish A? Nobody has actually gotten hurt, and B might not even know he was in danger. Moreover, say A unknowingly bought a defective gun that wouldn't shoot. Is he still guilty of attempted murder? Yep. Why? Because he had the required guilty state of mind but not only that he took action while having that guilty state of mind. We don't punish the state of mind by itself, we punish the convergence of guilty state of mind and action.
In this case, the people: 1) intended to smuggle illegally-taken lobster tails; and 2) actually imported the tails. The secret code they used and their failures to report are evidence that they knew or believed they were engaging in illegal activity. Should we punish them? Why not? How is this situation any different? The fact that the tails are legal under Honduran law is merely a fact like the inoperable gun in the previous example.