Death sticks were like the heroin of the Star Wars universe, but instead of just killing you they also fucked up your connection with the Force, if you had any. Most of the Jedi, including Mace Windu, smoked them, and they all got PWNed. Coincidence? I think not. Seriously, smoke these, and you're practically dead meat the next time you encounter a Sith lord, no matter how arrogant, big headed, and "cool" you are.
Allegedly, the smuggling of death sticks pissed off the Twi'leks, as it kinda ruined their spice smuggling operations. So the Twi'leks killed anyone they caught smuggling death sticks. The fact that the Twi'leks hated these things was one of the reasons why Darth Elmo paid people to smuggle them into areas where the Twi'leks were active. The Twi'leks would then intercept the shipment of death sticks and Darth Elmo could then kill the Twi'leks. The other reason Elmo had for smuggling death sticks was because it was an easy way to make money.