Earlier quoted context omitted.
Is it naïve to think that clinical trials have show that modern medicine is more effective? And the active molecules in those plants have been identified and can probably in many cases be synthesized more easily than extracted from the plants.
While I think the assessment that modern medicine is more effective, and often stands on the shoulders of these types of historically used plants, not everyone has safe access to modern medicine (either because "modern" medical treatments aren't available where they're located, lack of finances to pay for it in egregiously overpriced areas, or general mistreatment by the medical community). Using alternatives, while…
This isn't a choice between "cough medicine" and "slightly less effective cough medicine", it's a choice between a controlled and inspected product and random plants that may or may not be the right genus, dose and concentration.