Because street fentanyl is currently illegal, it has zero quality control, and people wind up dead taking doses that they didn't intend. Because it contaminates other drugs, people who don't intend to take fentanyl sometimes wind up dead from it.

We would be better off if people could purchase drugs legally from places that have stringent quality control so doses could be properly controlled.

that's what i've been saying for a long time, the problem isn't the pharamustical grade fentanyl, it's the street fentanyl thats problem, essentially because drug dealers have no quality control. Also cold comfort that the Scientist are with me. There's no drug that has ever become safer by ceding the market to criminals by way of prohibition. Every single one of them has gotten worse under such a regime. Look at Krokodil, that's the result of the inability to afford the real thing, and largely because of regulations on the chemical precursors.