A government could allow scientists to experiment without legal repercussions, but that doesn't eliminate ethics. Ethics we have either been born with or taught our whole lives cannot be thrown away at the drop of a hat. This scenario would be near impossible.
Scientists are currently operating on the idea that quantum indeterminism is true, having performed several studies on the molecular level, but either way, we still probably don't have free will. Neither determinism nor indeterminism is completely compatible with free will.
Antithesis: Illegal drugs are mostly illegal because of how harmful they can be,take heroin for example,the use of heroin is extremely dangerous (see sources) with PCP is the same,leading to potentionally psychosis,therefore so it isn't sold outside it should also be restricted to use right ther
Regulated use of drugs in itself is a good thing, it guarantees that it isn't cut with dangerous things and just makes the consumption of them safer (for example restricting the use of them to people with history of mental health problems), and hallucinogens (only some of them) aren't addictive