Would you say the same in regards to caffeine, alcohol?
There are genuine use cases for cannabis, one such example is enabling sufferers of chronic pain to have access to a far less dangerous method of pain relief compared to commonly prescribed opiates.
Legalisation of cannabis also ensures recreational users to contribute to the economy and have access to safely produced plants, this in itself acts as harm reduction.
Bad at what? Typically when a compound is considered a "drug" it's - by definition - because it has an effect on the body/mind.
Like the old joke says: why do people use drugs? Because they work!
If I take an ibuprofen and it doesn't diminish my headache, then I'd consider it "bad". If I am nauseous or insomniac and take a capsule containing cannabinoids which settles my stomach or relaxes me to sleep, then I'd consider it "good".
What I imagine you're saying is that "ingesting drugs for some things is good, but ingesting them to relax, wake up, or otherwise feel differently than you currently do is bad".
78% of our atmosphere is nitrogen, a known narcotic that has cost thousands of lives by inducing mental impairment in situations already fraught with hazard.
