In some circles (truckers and construction workers), use of meth can directly translate into less sleep and therefore more money. And yes, I still think recreational meth users would also still exist. Never underestimate the self-destructive capacity of addictive behavior/personality.

I don't know what your response is meant to convey. Are you implying that legalizing heroin would be great to stem the tide of meth abuse?

First off, very few people would use heroin if opium were legal. But even ignoring that, heroin is one of the safest drugs there is. There are virtually no longterm negative effects on physical or mental health[1], and it's almost impossible to accidentally O.D. on, especially if you're doing it with folks who have access to naloxone. Of the 500k+ current users, there are only ~200 deaths per year from heroin[2], and a good chunk of those are suicides. In other words, it's perhaps 25x safer than smoking American cigarrettes.

[1] C.f. The Consumer Union Guide to Licit and Illicit Drugs.

[2] Not counting polydrug deaths.