It is a misconception that 'low quality' drugs are ergo more dangerous. The only way that this would be true would be if the drug was replaced with a chemical that was itself more dangerous than the original drug, or had some kind of weird reaction, or there was some kind of inherintely dangerous containment from the production process.
Obviously this presents its own problems, but low quality does not neccesarily = more danger. It might just mean less active chemicals.
The reason people die of cocaine is often cardiac issues arising from the actual pharmacological properties of the chemical cocaine itself.