Not at all. There are plenty of people using heroin that are not your typical junkie, just like there are many recreatioal weed users that aren't unemployed stoners. Take me - I've been working in IT for twenty years, and have been a heroin addict for just about the same length of time. My career is going pretty well, I'm in charge of a team of engineers, I speak about my particular subject at conferences around the world regularly, I have plenty of work up on GitHub that people use.
What does kill people is stigmatizing addicts, and preventing them from getting the help they need to allow them to live a normal life and become usefully employed. Instead, attitudes like yours mean they are forced to become criminals and marginalized.
As far as I could tell it was common knowledge that the cartels would turn to some other source of income if cannabis was legalized in the US. It was unclear exactly what, but corruption and violence would still play a part as they were large parts of how the cartels functioned.
OR, OR, they could stop manufacturing poison and perhaps get a legitimate job and stop making money off of people with serious problems.
Weed doesn't kill.... heroin does nothing but kill. I guess I can't lay the blame totally on the manufacturers, but my god.... quit acting like their careers somehow deserve to exist one way or another and it's the USA's fault.