This incident does not show how legalizing drugs would result in this, just as drunk driving does not show how legalizing alcohol results in that. Personal responsibility and choices are what causes those events. The guy that shot his friend was already not “allowed” to have the drug in question, but did. He chose to break the law, he chose to use the drug, he chose to be irresponsible and caused the death of his friend.
As to testing for drugs in a traffic incident, the drugs do not matter, the incident matters. People have car crashes while sober, the result is the same. The same goes for other crimes, we all state it isn’t the firearm that kills, its the person using it that kills. People use all sorts of implements to kill, including hands, feet, and fists (a category in the FBI UCR stats). It does not matter what implement, or not, was used, the result is the same. The responsible party is the person, not the implement, same with drug use.
Did I state that drugs should not be tested and regulated? Are illegal drugs being tested and regulated now? Is Moonshine tested and regulated? As you pointed out, the government cannot control everything, and as a result, we must rely on ourselves and our judgment for day-to-day life. Is the Justice system “fair and just”? We read numerous cases where it does not appear to be, but we are not dissolving it, nor should we.
The War on Drugs is a horribly failed system that untold billions, probably trillions of dollars have vanished into, and lives lost on all sides, family members, criminals, police, etc. It did not prevent this person from obtaining illegal drugs and using them, nor prevent his killing his friend, nor will it prevent all the suffering of untold others. We should use that money for education and rehabilitation, that will help far more than incarcerating a drug user. Possession should not be a crime, only actual crimes should be prosecuted.