On meth: remember in the US this is a legally prescribed medication, and effectively indistinguishable from other amphetamines such as the Adderall mixture. There are plenty of professionals using amphetamines. The difference is probably that they're not smoking it for a rush, but using it to gain a long mental advantage. They're certainly very functional.

On heroin: Opiates are far less harmful than smoking, as long as you don't overdose (which is often caused by improper labeling or mixing with other drugs). You'd be surprised how many professionals are using opiates (such as time-release oxycodone) daily. Again, the difference is in using it for the mental advantage, not IV'ing it to get a rush and high.

It's just that in general, you're not going to have such people confess their usage due to negative social stigma. Thus the only "addicts" you see, are the ones that couldn't hold a job, couldn't get a supply (it's generally easier to buy heroin than proper opiate pills), and so on.