I think people are easier to control, but less productive when they have drugs. So it's really a question of what your nation is optimizing for at the time.
Of course having a sub-class of previously convicted minor offenders, who as a result struggle with work/life, can also be fairly effective. It's not exactly slavery - that was mostly their ancestors.
This is an opinion.
My opinion about your opinion is that your opinion is completely dumb and completely unfounded.
Michael Phelps smokes marijuana...along with countless other extremely high performers, doctor's, lawyers, politicians,movie stars, scientists Nobel prize winners, etc.
As for saying that executing drug offenders 'works'....I can't think of anything I've ever heard that's dumber in my life.
Especially when you could just execute ANYONE for breaking a law and keep the jails completely empty!
Why would you be so weak on crime?