Even if opium is nontoxic to tissue, what effect does it have on human abilities and behaviors? Water is nontoxic and has very little impact on abilities and behaviors. Is opium just like water?
What I'm trying to get you to admit is that there is one very specific biological impact of opioids -- their very strong tendency to activite or create dependency circuits in the brain, with a whole train of strong consequences that cannot logically be separated from the substance itself and the brain reactions it engenders.
How good are opium addicts at holding down jobs? At conducting healthy modern interpersonal relationships? At contributing to their communities and political systems? At raising children? Would you feel happy if your kid became an opium addict?