What are the ethics for preventing a mentally stable, tax paying adult from consuming whatever mind altering chemical they want?
With full knowledge of what could happen (because effects are often not uniform), and with the right care and support I would think it can be done ethically.
Look at the trials of using LSD/mushrooms/MDMA to help people work through serious trauma. Done well it looks to be positively life changing, done poorly and it seems to be horrifying.