A supply does not create a demand. The demand has to be there first.
Nicholas Murray was an adult, responsible for his own actions. He said, "Please provide this product," and a seller obliged.
The law may catch the seller and put him behind bars. If your case is strong enough, you can always take it to the civil courts and sue the seller...
...but the law, as it currently stands, is correct. Nicholas Murray was at least 50% responsible for his own death, perhaps even 100%. (e.g., if someone sells you four seconols but you opt to down them with a pint of Vodka, who is to blame when your lungs and heart stop functioning?)
Let me offer you another perspective: If I drink a quart of Wild Turkey and die of alcohol poisoning, should the ABC Store or the salesman be prosecuted for murder?
Drug sales follow the laws of supply and demand