What if a product like cocaine were legal in developing country A (where producers are), but illegal in developed country B (where consumers are)?
Probably this situation would be similar to immigration. Immigrants are legal in their native country (A), but some of them are illegal in country B, where there is demand for them. They have high incentives to immigrate because in country B they can earn much more than they do in country A.
We don't see much violence related to immigration in sending countries. We probably would not see much violence related to cocaine in sending countries either, if it were legal there.