Maybe less dangerous in the immediate term from overdose, but isn't ketamine potentially rather dangerous to the brain? Wikipedia seems to suggest that frequent ketamine usage causes memory issues, and there might be possible brain damage.
Whereas opiates, to my knowledge, don't actually have any serious side effects, or long term health issues (apart from constipation and perhaps lowered testosterone). Apart from the overdose risk, that is.
Ketamine blocks the NMDA receptor, which is thought to be the receptor that causes memory formation. So it is expected to affect memory.
The brain damage effect is uncharacterized in humans. Several NMDA drugs cause this effect in rats, but none of them have been found to cause devastating problems in humans except PCP.
There is some suggestion that opioids cause cancer, but the only study was small and observational.
Whereas opiates, to my knowledge, don't actually have any serious side effects, or long term health issues (apart from constipation and perhaps lowered testosterone). Apart from the overdose risk, that is.