I've had friends who've died from purchasing bad drugs at raves from people who were looking to make money and run. In one situation it ended up being rat poison. The guy had other drugs in his system, and combined with the poison his body went into shock. With darknet markets and independent lab testing networks, this type of thing doesn't happen.
People are still going to use drugs. I'd rather law enforcement go after the guys who are selling rat poison at raves than the guys who are setting up safe distribution networks.
It is not a reasonable argument for an individual to make to try to justify their illegal get-rich scheme.
Whether true or not, the intention behind drug laws is physical harm and addiction. Additional harms like risk of violence or overdoses due to impurities are secondary at best.
Unless there's judicial activism going on, making that admission is pretty much just handing the keys to freedom over. Why even bother with a trial? Should have done a plea bargain.