[dragonwriter]

> Wouldn't even the shadiest of dealers want to keep their customers/hosts/victims around to, you know, keep bleeding money?

Most illegal drugs are potentially deadly, and some share of users are going to die from them. Even rationally, cutting with cheaper but more toxic material can be justified if the increase in profit per transaction is sufficient to outweigh the reduction in the expected number of transactions per customer.

Of course, also, drug dealers may not always act rationally, and may not even understand the hazards (either in isolation or due to combination with the drug in question) posed by ingredients used to cut drugs.