I will type this very slowly so maybe you will understand. What was done was done illegally under International Law. The drug lords, if that was actually on the boat, are not at war with the US. The most expedient thing to do was to keep track of the vessel, and when it came into US waters have the Coast Guard board it, seize the contents and arrest everyone on the ship.
In essence we stopped one shipload of drugs, killed a bunch of people.Big Deal. It's why we're losing the War on Drugs because of shortsightedness by people like you. But the bottom line is that was only one shipment. Go after the head of the snake, not the tail. This action only made the Drug Lords more determined.