I disagree. If you take [action], and it was a necessary and sufficient condition for [consequence], then you are morally responsible for that consequence. (Sure, the individuals committing crimes in this concrete case are also morally respoinsible). In this case, I think it is correct to say that the laws cause violence, since that violence would not be happening otherwise.

There is a common trope that criminals sit down and decide what crime they will commit, and decide that drug dealing is the best one. In fact, that is backwards; if the TAM of crime is cut by 10x, then there are fewer jobs, and at the margin some will stop. And in the other direction, if there is no longer easy money to be made by selling drugs, then fewer would find their way into the drug business in the first place.

See prohibition in the USA for a natural experiment that supports my claims here.