If someone breaks the law by jaywalking, and a driver of a car runs him over when he could have avoiding hitting him (by braking) is it likewise unwarranted to shift the blame for the poor decisions of the jaywalker onto the driver?
If not, what is the reason you decide the two situations differently?
In the law, the jaywalker and the driver will share responsibility. If you knowingly sell carfentanil, the mechanism by which the law apportions blame onto the "victim" won't exist: there is no set plausible of circumstances in which you could reasonably believe it was OK to sell someone carfentanil, where in the jaywalking case there are dueling factors of pedestrial negligence and driver duty of care.
I don't think the analogy holds. A drug user wants to buy from the dealer. The dealer is providing a service that the drug user can voluntarily turn down.
I don't see how that's similar to a driver running into a jaywalker. Just because he's jaywalking doesn't mean he wants a driver to hit him.