Drug users and their suppliers have one thing in common; they are both totally selfish.
To the supplier, the end always justifies the means. If some politician goes after them, his family could be kidnapped. In which case the cartels go after their extended family. If as has been suggested, some poisoned drugs were circulated, these might be forced onto those kidnapped.
The drug user will happily take drugs on the basis that, 'I won't become an addict, they won't make me paranoid'. By they time they discover that they are one of those who is really badly affected by them, it is too late, and their relatives and society as a whole is left to pick up the bill for their long term care.
Legalising the supply may get rid of the illegal drugs cartels, but what do we do about the users who become paranoid and incapable of work? Tell them they knew the risk, they took it and we aren't prepared to support them and will have them put down?