It's a fact of life: Whenever uptight governments forbid certain goods on their worlds, demand for these items increases. Once demand turns profitable, enterprising starship captains risk everything to deliver the goods in question.
Careers in smuggling are fast-paced, thrilling and often short-lived. Running contraband not only places a smuggler at odds with a planet's law enforcement, but its criminal elements as well. Pirates, gangsters, revolutionaries and bounty hunters are just a few of the hazards standing between a smuggler and that big payday. Only those who possess the sharpest instincts, sturdiest freighters and quickest blasters live long enough to earn a good living at this game.
It's worth noting that not all smugglers are profiteers. Some style themselves as heroic blockade runners or patriotic privateers, delivering hope and much-needed supplies to those who need it. Of course, that's also exactly how the real criminal types describe themselves, and law enforcement officers rarely accept “I was serving a noble cause” as an excuse.